diff --git a/library/CHANGELOG.md b/library/CHANGELOG.md
index 099bc9812..92f1ce498 100644
--- a/library/CHANGELOG.md
+++ b/library/CHANGELOG.md
@@ -5,6 +5,7 @@ All notable changes to the library will be documented in this file.
 ## vX.X.X (Month DD, YYYY)
 
 - Add `nanoid` action to validate Nano IDs (pull request #789)
+- Add `undefinedable` and `undefinedableAsync` schema (issue #385)
 
 ## v0.39.0 (August 24, 2024)
 
diff --git a/library/src/methods/getDefault/getDefault.ts b/library/src/methods/getDefault/getDefault.ts
index c3a326dc4..7a21a8978 100644
--- a/library/src/methods/getDefault/getDefault.ts
+++ b/library/src/methods/getDefault/getDefault.ts
@@ -5,6 +5,8 @@ import type {
   NullishSchemaAsync,
   OptionalSchema,
   OptionalSchemaAsync,
+  UndefinedableSchema,
+  UndefinedableSchemaAsync,
 } from '../../schemas/index.ts';
 import type {
   BaseIssue,
@@ -41,6 +43,15 @@ export type InferDefault<
         | BaseSchema<unknown, unknown, BaseIssue<unknown>>
         | BaseSchemaAsync<unknown, unknown, BaseIssue<unknown>>,
         unknown
+      >
+    | UndefinedableSchema<
+        BaseSchema<unknown, unknown, BaseIssue<unknown>>,
+        unknown
+      >
+    | UndefinedableSchemaAsync<
+        | BaseSchema<unknown, unknown, BaseIssue<unknown>>
+        | BaseSchemaAsync<unknown, unknown, BaseIssue<unknown>>,
+        unknown
       >,
 > = TSchema extends
   | NullableSchema<
@@ -70,6 +81,15 @@ export type InferDefault<
       | BaseSchemaAsync<unknown, unknown, BaseIssue<unknown>>,
       infer TDefault
     >
+  | UndefinedableSchema<
+      BaseSchema<unknown, unknown, BaseIssue<unknown>>,
+      infer TDefault
+    >
+  | UndefinedableSchemaAsync<
+      | BaseSchema<unknown, unknown, BaseIssue<unknown>>
+      | BaseSchemaAsync<unknown, unknown, BaseIssue<unknown>>,
+      infer TDefault
+    >
   ? [TDefault] extends [never]
     ? undefined
     : TDefault extends () => MaybePromise<InferInput<TSchema>>
diff --git a/library/src/methods/unwrap/unwrap.ts b/library/src/methods/unwrap/unwrap.ts
index 84b860f4d..53bbb03cb 100644
--- a/library/src/methods/unwrap/unwrap.ts
+++ b/library/src/methods/unwrap/unwrap.ts
@@ -14,6 +14,8 @@ import type {
   NullishSchemaAsync,
   OptionalSchema,
   OptionalSchemaAsync,
+  UndefinedableSchema,
+  UndefinedableSchemaAsync,
 } from '../../schemas/index.ts';
 import type {
   BaseIssue,
@@ -75,6 +77,15 @@ export function unwrap<
         | BaseSchema<unknown, unknown, BaseIssue<unknown>>
         | BaseSchemaAsync<unknown, unknown, BaseIssue<unknown>>,
         unknown
+      >
+    | UndefinedableSchema<
+        BaseSchema<unknown, unknown, BaseIssue<unknown>>,
+        unknown
+      >
+    | UndefinedableSchemaAsync<
+        | BaseSchema<unknown, unknown, BaseIssue<unknown>>
+        | BaseSchemaAsync<unknown, unknown, BaseIssue<unknown>>,
+        unknown
       >,
 >(schema: TSchema): TSchema['wrapped'] {
   return schema.wrapped;
diff --git a/library/src/schemas/index.ts b/library/src/schemas/index.ts
index 320e668b8..9bb5c495c 100644
--- a/library/src/schemas/index.ts
+++ b/library/src/schemas/index.ts
@@ -38,6 +38,7 @@ export * from './symbol/index.ts';
 export * from './tuple/index.ts';
 export * from './tupleWithRest/index.ts';
 export * from './undefined/index.ts';
+export * from './undefinedable/index.ts';
 export * from './union/index.ts';
 export * from './unknown/index.ts';
 export * from './variant/index.ts';
diff --git a/library/src/schemas/looseObject/looseObject.test-d.ts b/library/src/schemas/looseObject/looseObject.test-d.ts
index c18fd7ac4..05284b2eb 100644
--- a/library/src/schemas/looseObject/looseObject.test-d.ts
+++ b/library/src/schemas/looseObject/looseObject.test-d.ts
@@ -11,6 +11,7 @@ import {
   type StringIssue,
   type StringSchema,
 } from '../string/index.ts';
+import type { UndefinedableSchema } from '../undefinedable/index.ts';
 import { looseObject, type LooseObjectSchema } from './looseObject.ts';
 import type { LooseObjectIssue } from './types.ts';
 
@@ -46,6 +47,7 @@ describe('looseObject', () => {
         key3: NullishSchema<StringSchema<undefined>, never>;
         key4: ObjectSchema<{ key: NumberSchema<undefined> }, never>;
         key5: SchemaWithPipe<[StringSchema<undefined>, ReadonlyAction<string>]>;
+        key6: UndefinedableSchema<StringSchema<undefined>, 'bar'>;
       },
       undefined
     >;
@@ -55,9 +57,10 @@ describe('looseObject', () => {
         {
           key1: string;
           key2?: string;
-          key3?: string | null;
+          key3?: string | null | undefined;
           key4: { key: number };
           key5: string;
+          key6: string | undefined;
         } & { [key: string]: unknown }
       >();
     });
@@ -67,9 +70,10 @@ describe('looseObject', () => {
         {
           key1: string;
           key2: string;
-          key3?: string | null;
+          key3?: string | null | undefined;
           key4: { key: number };
           readonly key5: string;
+          key6: string;
         } & { [key: string]: unknown }
       >();
     });
diff --git a/library/src/schemas/looseObject/looseObject.test.ts b/library/src/schemas/looseObject/looseObject.test.ts
index 13dffdd2c..00588f5d3 100644
--- a/library/src/schemas/looseObject/looseObject.test.ts
+++ b/library/src/schemas/looseObject/looseObject.test.ts
@@ -143,7 +143,6 @@ describe('looseObject', () => {
     test('for nullish entry', () => {
       expectNoSchemaIssue(looseObject({ key: nullish(number()) }), [
         {},
-        // @ts-expect-error
         { key: undefined },
         { key: null },
         { key: 123 },
diff --git a/library/src/schemas/looseObject/looseObjectAsync.test-d.ts b/library/src/schemas/looseObject/looseObjectAsync.test-d.ts
index 3f8e89efd..44b56bfa6 100644
--- a/library/src/schemas/looseObject/looseObjectAsync.test-d.ts
+++ b/library/src/schemas/looseObject/looseObjectAsync.test-d.ts
@@ -11,6 +11,7 @@ import {
   type StringIssue,
   type StringSchema,
 } from '../string/index.ts';
+import type { UndefinedableSchema } from '../undefinedable/index.ts';
 import {
   looseObjectAsync,
   type LooseObjectSchemaAsync,
@@ -51,6 +52,7 @@ describe('looseObjectAsync', () => {
         key3: NullishSchema<StringSchema<undefined>, never>;
         key4: ObjectSchema<{ key: NumberSchema<undefined> }, never>;
         key5: SchemaWithPipe<[StringSchema<undefined>, ReadonlyAction<string>]>;
+        key6: UndefinedableSchema<StringSchema<undefined>, 'bar'>;
       },
       undefined
     >;
@@ -60,9 +62,10 @@ describe('looseObjectAsync', () => {
         {
           key1: string;
           key2?: string;
-          key3?: string | null;
+          key3?: string | null | undefined;
           key4: { key: number };
           key5: string;
+          key6: string | undefined;
         } & { [key: string]: unknown }
       >();
     });
@@ -72,9 +75,10 @@ describe('looseObjectAsync', () => {
         {
           key1: string;
           key2: string;
-          key3?: string | null;
+          key3?: string | null | undefined;
           key4: { key: number };
           readonly key5: string;
+          key6: string;
         } & { [key: string]: unknown }
       >();
     });
diff --git a/library/src/schemas/looseObject/looseObjectAsync.test.ts b/library/src/schemas/looseObject/looseObjectAsync.test.ts
index c21648b12..31ab43ca2 100644
--- a/library/src/schemas/looseObject/looseObjectAsync.test.ts
+++ b/library/src/schemas/looseObject/looseObjectAsync.test.ts
@@ -165,13 +165,7 @@ describe('looseObjectAsync', () => {
     test('for nullish entry', async () => {
       await expectNoSchemaIssueAsync(
         looseObjectAsync({ key: nullish(number()) }),
-        [
-          {},
-          // @ts-expect-error
-          { key: undefined },
-          { key: null },
-          { key: 123 },
-        ]
+        [{}, { key: undefined }, { key: null }, { key: 123 }]
       );
     });
 
diff --git a/library/src/schemas/object/object.test-d.ts b/library/src/schemas/object/object.test-d.ts
index cc60f792a..51e13c917 100644
--- a/library/src/schemas/object/object.test-d.ts
+++ b/library/src/schemas/object/object.test-d.ts
@@ -10,6 +10,7 @@ import {
   type StringIssue,
   type StringSchema,
 } from '../string/index.ts';
+import type { UndefinedableSchema } from '../undefinedable/index.ts';
 import { object, type ObjectSchema } from './object.ts';
 import type { ObjectIssue } from './types.ts';
 
@@ -45,6 +46,7 @@ describe('object', () => {
         key3: NullishSchema<StringSchema<undefined>, never>;
         key4: ObjectSchema<{ key: NumberSchema<undefined> }, never>;
         key5: SchemaWithPipe<[StringSchema<undefined>, ReadonlyAction<string>]>;
+        key6: UndefinedableSchema<StringSchema<undefined>, 'bar'>;
       },
       undefined
     >;
@@ -53,9 +55,10 @@ describe('object', () => {
       expectTypeOf<InferInput<Schema>>().toEqualTypeOf<{
         key1: string;
         key2?: string;
-        key3?: string | null;
+        key3?: string | null | undefined;
         key4: { key: number };
         key5: string;
+        key6: string | undefined;
       }>();
     });
 
@@ -63,9 +66,10 @@ describe('object', () => {
       expectTypeOf<InferOutput<Schema>>().toEqualTypeOf<{
         key1: string;
         key2: string;
-        key3?: string | null;
+        key3?: string | null | undefined;
         key4: { key: number };
         readonly key5: string;
+        key6: string;
       }>();
     });
 
diff --git a/library/src/schemas/object/object.test.ts b/library/src/schemas/object/object.test.ts
index 7a224db2a..bba8b11e6 100644
--- a/library/src/schemas/object/object.test.ts
+++ b/library/src/schemas/object/object.test.ts
@@ -148,7 +148,6 @@ describe('object', () => {
     test('for nullish entry', () => {
       expectNoSchemaIssue(object({ key: nullish(number()) }), [
         {},
-        // @ts-expect-error
         { key: undefined },
         { key: null },
         { key: 123 },
diff --git a/library/src/schemas/object/objectAsync.test-d.ts b/library/src/schemas/object/objectAsync.test-d.ts
index 429ef7c8e..ea891e200 100644
--- a/library/src/schemas/object/objectAsync.test-d.ts
+++ b/library/src/schemas/object/objectAsync.test-d.ts
@@ -10,6 +10,7 @@ import {
   type StringIssue,
   type StringSchema,
 } from '../string/index.ts';
+import type { UndefinedableSchema } from '../undefinedable/index.ts';
 import { objectAsync, type ObjectSchemaAsync } from './objectAsync.ts';
 import type { ObjectIssue } from './types.ts';
 
@@ -45,6 +46,7 @@ describe('objectAsync', () => {
         key3: NullishSchema<StringSchema<undefined>, never>;
         key4: ObjectSchemaAsync<{ key: NumberSchema<undefined> }, never>;
         key5: SchemaWithPipe<[StringSchema<undefined>, ReadonlyAction<string>]>;
+        key6: UndefinedableSchema<StringSchema<undefined>, 'bar'>;
       },
       undefined
     >;
@@ -53,9 +55,10 @@ describe('objectAsync', () => {
       expectTypeOf<InferInput<Schema>>().toEqualTypeOf<{
         key1: string;
         key2?: string;
-        key3?: string | null;
+        key3?: string | null | undefined;
         key4: { key: number };
         key5: string;
+        key6: string | undefined;
       }>();
     });
 
@@ -63,9 +66,10 @@ describe('objectAsync', () => {
       expectTypeOf<InferOutput<Schema>>().toEqualTypeOf<{
         key1: string;
         key2: string;
-        key3?: string | null;
+        key3?: string | null | undefined;
         key4: { key: number };
         readonly key5: string;
+        key6: string;
       }>();
     });
 
diff --git a/library/src/schemas/object/objectAsync.test.ts b/library/src/schemas/object/objectAsync.test.ts
index 70978928e..d58038a25 100644
--- a/library/src/schemas/object/objectAsync.test.ts
+++ b/library/src/schemas/object/objectAsync.test.ts
@@ -160,7 +160,6 @@ describe('objectAsync', () => {
     test('for nullish entry', async () => {
       await expectNoSchemaIssueAsync(objectAsync({ key: nullish(number()) }), [
         {},
-        // @ts-expect-error
         { key: undefined },
         { key: null },
         { key: 123 },
diff --git a/library/src/schemas/objectWithRest/objectWithRest.test-d.ts b/library/src/schemas/objectWithRest/objectWithRest.test-d.ts
index aa858fff3..6464c4ee8 100644
--- a/library/src/schemas/objectWithRest/objectWithRest.test-d.ts
+++ b/library/src/schemas/objectWithRest/objectWithRest.test-d.ts
@@ -16,6 +16,7 @@ import {
   type StringIssue,
   type StringSchema,
 } from '../string/index.ts';
+import type { UndefinedableSchema } from '../undefinedable/index.ts';
 import { objectWithRest, type ObjectWithRestSchema } from './objectWithRest.ts';
 import type { ObjectWithRestIssue } from './types.ts';
 
@@ -55,6 +56,7 @@ describe('objectWithRest', () => {
         key3: NullishSchema<StringSchema<undefined>, never>;
         key4: ObjectSchema<{ key: NumberSchema<undefined> }, never>;
         key5: SchemaWithPipe<[StringSchema<undefined>, ReadonlyAction<string>]>;
+        key6: UndefinedableSchema<StringSchema<undefined>, 'bar'>;
       },
       BooleanSchema<undefined>,
       undefined
@@ -65,9 +67,10 @@ describe('objectWithRest', () => {
         {
           key1: string;
           key2?: string;
-          key3?: string | null;
+          key3?: string | null | undefined;
           key4: { key: number };
           key5: string;
+          key6: string | undefined;
         } & { [key: string]: boolean }
       >();
     });
@@ -77,9 +80,10 @@ describe('objectWithRest', () => {
         {
           key1: string;
           key2: string;
-          key3?: string | null;
+          key3?: string | null | undefined;
           key4: { key: number };
           readonly key5: string;
+          key6: string;
         } & { [key: string]: boolean }
       >();
     });
diff --git a/library/src/schemas/objectWithRest/objectWithRestAsync.test-d.ts b/library/src/schemas/objectWithRest/objectWithRestAsync.test-d.ts
index d564d8263..fd75024a5 100644
--- a/library/src/schemas/objectWithRest/objectWithRestAsync.test-d.ts
+++ b/library/src/schemas/objectWithRest/objectWithRestAsync.test-d.ts
@@ -16,6 +16,7 @@ import {
   type StringIssue,
   type StringSchema,
 } from '../string/index.ts';
+import type { UndefinedableSchema } from '../undefinedable/index.ts';
 import {
   objectWithRestAsync,
   type ObjectWithRestSchemaAsync,
@@ -58,6 +59,7 @@ describe('objectWithRestAsync', () => {
         key3: NullishSchema<StringSchema<undefined>, never>;
         key4: ObjectSchema<{ key: NumberSchema<undefined> }, never>;
         key5: SchemaWithPipe<[StringSchema<undefined>, ReadonlyAction<string>]>;
+        key6: UndefinedableSchema<StringSchema<undefined>, 'bar'>;
       },
       BooleanSchema<undefined>,
       undefined
@@ -68,9 +70,10 @@ describe('objectWithRestAsync', () => {
         {
           key1: string;
           key2?: string;
-          key3?: string | null;
+          key3?: string | null | undefined;
           key4: { key: number };
           key5: string;
+          key6: string | undefined;
         } & { [key: string]: boolean }
       >();
     });
@@ -80,9 +83,10 @@ describe('objectWithRestAsync', () => {
         {
           key1: string;
           key2: string;
-          key3?: string | null;
+          key3?: string | null | undefined;
           key4: { key: number };
           readonly key5: string;
+          key6: string;
         } & { [key: string]: boolean }
       >();
     });
diff --git a/library/src/schemas/record/types.ts b/library/src/schemas/record/types.ts
index c21583110..b378e34fd 100644
--- a/library/src/schemas/record/types.ts
+++ b/library/src/schemas/record/types.ts
@@ -1,4 +1,4 @@
-import type { Brand } from '../../actions/index.ts';
+import type { Brand, ReadonlyAction } from '../../actions/index.ts';
 import type {
   SchemaWithPipe,
   SchemaWithPipeAsync,
@@ -10,8 +10,6 @@ import type {
   InferInput,
   InferOutput,
   MarkOptional,
-  PipeItem,
-  PipeItemAsync,
   Prettify,
 } from '../../types/index.ts';
 
@@ -78,26 +76,10 @@ type WithReadonly<
     | BaseSchemaAsync<unknown, unknown, BaseIssue<unknown>>,
   TObject extends WithQuestionMarks<Record<string | number | symbol, unknown>>,
 > = TValue extends
-  | SchemaWithPipe<
-      [
-        BaseSchema<unknown, unknown, BaseIssue<unknown>>,
-        // eslint-disable-next-line @typescript-eslint/no-explicit-any
-        ...PipeItem<any, unknown, BaseIssue<unknown>>[],
-      ]
-    >
-  | SchemaWithPipeAsync<
-      [
-        (
-          | BaseSchema<unknown, unknown, BaseIssue<unknown>>
-          | BaseSchemaAsync<unknown, unknown, BaseIssue<unknown>>
-        ),
-        ...(
-          | PipeItem<any, unknown, BaseIssue<unknown>> // eslint-disable-line @typescript-eslint/no-explicit-any
-          | PipeItemAsync<any, unknown, BaseIssue<unknown>> // eslint-disable-line @typescript-eslint/no-explicit-any
-        )[],
-      ]
-    >
-  ? 'readonly' extends TValue['pipe'][number]['type']
+  | SchemaWithPipe<infer TPipe>
+  | SchemaWithPipeAsync<infer TPipe>
+  ? // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    ReadonlyAction<any> extends TPipe[number]
     ? Readonly<TObject>
     : TObject
   : TObject;
diff --git a/library/src/schemas/strictObject/strictObject.test-d.ts b/library/src/schemas/strictObject/strictObject.test-d.ts
index 72c9a531a..174b2abfb 100644
--- a/library/src/schemas/strictObject/strictObject.test-d.ts
+++ b/library/src/schemas/strictObject/strictObject.test-d.ts
@@ -11,6 +11,7 @@ import {
   type StringIssue,
   type StringSchema,
 } from '../string/index.ts';
+import type { UndefinedableSchema } from '../undefinedable/index.ts';
 import { strictObject, type StrictObjectSchema } from './strictObject.ts';
 import type { StrictObjectIssue } from './types.ts';
 
@@ -46,6 +47,7 @@ describe('strictObject', () => {
         key3: NullishSchema<StringSchema<undefined>, never>;
         key4: ObjectSchema<{ key: NumberSchema<undefined> }, never>;
         key5: SchemaWithPipe<[StringSchema<undefined>, ReadonlyAction<string>]>;
+        key6: UndefinedableSchema<StringSchema<undefined>, 'bar'>;
       },
       undefined
     >;
@@ -54,9 +56,10 @@ describe('strictObject', () => {
       expectTypeOf<InferInput<Schema>>().toEqualTypeOf<{
         key1: string;
         key2?: string;
-        key3?: string | null;
+        key3?: string | null | undefined;
         key4: { key: number };
         key5: string;
+        key6: string | undefined;
       }>();
     });
 
@@ -64,9 +67,10 @@ describe('strictObject', () => {
       expectTypeOf<InferOutput<Schema>>().toEqualTypeOf<{
         key1: string;
         key2: string;
-        key3?: string | null;
+        key3?: string | null | undefined;
         key4: { key: number };
         readonly key5: string;
+        key6: string;
       }>();
     });
 
diff --git a/library/src/schemas/strictObject/strictObject.test.ts b/library/src/schemas/strictObject/strictObject.test.ts
index 138736119..d5c1ae91a 100644
--- a/library/src/schemas/strictObject/strictObject.test.ts
+++ b/library/src/schemas/strictObject/strictObject.test.ts
@@ -137,7 +137,6 @@ describe('strictObject', () => {
     test('for nullish entry', () => {
       expectNoSchemaIssue(strictObject({ key: nullish(number()) }), [
         {},
-        // @ts-expect-error
         { key: undefined },
         { key: null },
         { key: 123 },
diff --git a/library/src/schemas/strictObject/strictObjectAsync.test-d.ts b/library/src/schemas/strictObject/strictObjectAsync.test-d.ts
index b1ef8c582..6a5ed5c8d 100644
--- a/library/src/schemas/strictObject/strictObjectAsync.test-d.ts
+++ b/library/src/schemas/strictObject/strictObjectAsync.test-d.ts
@@ -11,6 +11,7 @@ import {
   type StringIssue,
   type StringSchema,
 } from '../string/index.ts';
+import type { UndefinedableSchema } from '../undefinedable/index.ts';
 import {
   strictObjectAsync,
   type StrictObjectSchemaAsync,
@@ -51,6 +52,7 @@ describe('strictObjectAsync', () => {
         key3: NullishSchema<StringSchema<undefined>, never>;
         key4: ObjectSchema<{ key: NumberSchema<undefined> }, never>;
         key5: SchemaWithPipe<[StringSchema<undefined>, ReadonlyAction<string>]>;
+        key6: UndefinedableSchema<StringSchema<undefined>, 'bar'>;
       },
       undefined
     >;
@@ -59,9 +61,10 @@ describe('strictObjectAsync', () => {
       expectTypeOf<InferInput<Schema>>().toEqualTypeOf<{
         key1: string;
         key2?: string;
-        key3?: string | null;
+        key3?: string | null | undefined;
         key4: { key: number };
         key5: string;
+        key6: string | undefined;
       }>();
     });
 
@@ -69,9 +72,10 @@ describe('strictObjectAsync', () => {
       expectTypeOf<InferOutput<Schema>>().toEqualTypeOf<{
         key1: string;
         key2: string;
-        key3?: string | null;
+        key3?: string | null | undefined;
         key4: { key: number };
         readonly key5: string;
+        key6: string;
       }>();
     });
 
diff --git a/library/src/schemas/strictObject/strictObjectAsync.test.ts b/library/src/schemas/strictObject/strictObjectAsync.test.ts
index 4328ad92d..c548932c7 100644
--- a/library/src/schemas/strictObject/strictObjectAsync.test.ts
+++ b/library/src/schemas/strictObject/strictObjectAsync.test.ts
@@ -158,13 +158,7 @@ describe('strictObjectAsync', () => {
     test('for nullish entry', async () => {
       await expectNoSchemaIssueAsync(
         strictObjectAsync({ key: nullish(number()) }),
-        [
-          {},
-          // @ts-expect-error
-          { key: undefined },
-          { key: null },
-          { key: 123 },
-        ]
+        [{}, { key: undefined }, { key: null }, { key: 123 }]
       );
     });
   });
diff --git a/library/src/schemas/undefinedable/index.ts b/library/src/schemas/undefinedable/index.ts
new file mode 100644
index 000000000..5a26c14ef
--- /dev/null
+++ b/library/src/schemas/undefinedable/index.ts
@@ -0,0 +1,3 @@
+export * from './undefinedable.ts';
+export * from './undefinedableAsync.ts';
+export * from './types.ts';
diff --git a/library/src/schemas/undefinedable/types.ts b/library/src/schemas/undefinedable/types.ts
new file mode 100644
index 000000000..53692b0df
--- /dev/null
+++ b/library/src/schemas/undefinedable/types.ts
@@ -0,0 +1,24 @@
+import type {
+  BaseIssue,
+  BaseSchema,
+  BaseSchemaAsync,
+  DefaultAsync,
+  DefaultValue,
+  InferOutput,
+  NonOptional,
+} from '../../types/index.ts';
+
+/**
+ * Infer undefinedable output type.
+ */
+export type InferUndefinedableOutput<
+  TWrapped extends
+    | BaseSchema<unknown, unknown, BaseIssue<unknown>>
+    | BaseSchemaAsync<unknown, unknown, BaseIssue<unknown>>,
+  TDefault extends DefaultAsync<TWrapped, undefined>,
+> = [TDefault] extends [never]
+  ? InferOutput<TWrapped> | undefined
+  : // FIXME: For schemas that transform the input to `undefined`, this
+    // implementation may result in an incorrect output type
+    | NonOptional<InferOutput<TWrapped>>
+      | Extract<DefaultValue<TDefault>, undefined>;
diff --git a/library/src/schemas/undefinedable/undefinedable.test-d.ts b/library/src/schemas/undefinedable/undefinedable.test-d.ts
new file mode 100644
index 000000000..014c069a2
--- /dev/null
+++ b/library/src/schemas/undefinedable/undefinedable.test-d.ts
@@ -0,0 +1,78 @@
+import { describe, expectTypeOf, test } from 'vitest';
+import type { InferInput, InferIssue, InferOutput } from '../../types/index.ts';
+import {
+  string,
+  type StringIssue,
+  type StringSchema,
+} from '../string/index.ts';
+import { undefinedable, type UndefinedableSchema } from './undefinedable.ts';
+
+describe('undefinedable', () => {
+  describe('should return schema object', () => {
+    test('with never default', () => {
+      expectTypeOf(undefinedable(string())).toEqualTypeOf<
+        UndefinedableSchema<StringSchema<undefined>, never>
+      >();
+    });
+
+    test('with undefined default', () => {
+      expectTypeOf(undefinedable(string(), undefined)).toEqualTypeOf<
+        UndefinedableSchema<StringSchema<undefined>, undefined>
+      >();
+    });
+
+    test('with undefined getter default', () => {
+      expectTypeOf(undefinedable(string(), () => undefined)).toEqualTypeOf<
+        UndefinedableSchema<StringSchema<undefined>, () => undefined>
+      >();
+    });
+
+    test('with value default', () => {
+      expectTypeOf(undefinedable(string(), 'foo')).toEqualTypeOf<
+        UndefinedableSchema<StringSchema<undefined>, 'foo'>
+      >();
+    });
+
+    test('with value getter default', () => {
+      expectTypeOf(undefinedable(string(), () => 'foo')).toEqualTypeOf<
+        UndefinedableSchema<StringSchema<undefined>, () => string>
+      >();
+    });
+  });
+
+  describe('should infer correct types', () => {
+    type Schema1 = UndefinedableSchema<StringSchema<undefined>, never>;
+    type Schema2 = UndefinedableSchema<StringSchema<undefined>, undefined>;
+    type Schema3 = UndefinedableSchema<StringSchema<undefined>, 'foo'>;
+    type Schema4 = UndefinedableSchema<
+      StringSchema<undefined>,
+      () => undefined
+    >;
+    type Schema5 = UndefinedableSchema<StringSchema<undefined>, () => 'foo'>;
+
+    test('of input', () => {
+      type Input = string | undefined;
+      expectTypeOf<InferInput<Schema1>>().toEqualTypeOf<Input>();
+      expectTypeOf<InferInput<Schema2>>().toEqualTypeOf<Input>();
+      expectTypeOf<InferInput<Schema3>>().toEqualTypeOf<Input>();
+      expectTypeOf<InferInput<Schema4>>().toEqualTypeOf<Input>();
+      expectTypeOf<InferInput<Schema5>>().toEqualTypeOf<Input>();
+    });
+
+    test('of output', () => {
+      expectTypeOf<InferOutput<Schema1>>().toEqualTypeOf<string | undefined>();
+      expectTypeOf<InferOutput<Schema2>>().toEqualTypeOf<string | undefined>();
+      expectTypeOf<InferOutput<Schema3>>().toEqualTypeOf<string>();
+      expectTypeOf<InferOutput<Schema4>>().toEqualTypeOf<string | undefined>();
+      expectTypeOf<InferOutput<Schema5>>().toEqualTypeOf<string>();
+    });
+
+    test('of issue', () => {
+      expectTypeOf<InferIssue<Schema1>>().toEqualTypeOf<StringIssue>();
+      expectTypeOf<InferIssue<Schema2>>().toEqualTypeOf<StringIssue>();
+      expectTypeOf<InferIssue<Schema3>>().toEqualTypeOf<StringIssue>();
+      expectTypeOf<InferIssue<Schema4>>().toEqualTypeOf<StringIssue>();
+      expectTypeOf<InferIssue<Schema5>>().toEqualTypeOf<StringIssue>();
+    });
+  });
+});
diff --git a/library/src/schemas/undefinedable/undefinedable.test.ts b/library/src/schemas/undefinedable/undefinedable.test.ts
new file mode 100644
index 000000000..645e2ef17
--- /dev/null
+++ b/library/src/schemas/undefinedable/undefinedable.test.ts
@@ -0,0 +1,109 @@
+import { describe, expect, test } from 'vitest';
+import { expectNoSchemaIssue } from '../../vitest/index.ts';
+import { string, type StringSchema } from '../string/index.ts';
+import { undefinedable, type UndefinedableSchema } from './undefinedable.ts';
+
+describe('undefinedable', () => {
+  describe('should return schema object', () => {
+    const baseSchema: Omit<
+      UndefinedableSchema<StringSchema<undefined>, string>,
+      'default'
+    > = {
+      kind: 'schema',
+      type: 'undefinedable',
+      reference: undefinedable,
+      expects: '(string | undefined)',
+      wrapped: { ...string(), _run: expect.any(Function) },
+      async: false,
+      _run: expect.any(Function),
+    };
+
+    test('with never default', () => {
+      expect(undefinedable(string())).toStrictEqual(baseSchema);
+    });
+
+    test('with undefined default', () => {
+      expect(undefinedable(string(), undefined)).toStrictEqual({
+        ...baseSchema,
+        default: undefined,
+      } satisfies UndefinedableSchema<StringSchema<undefined>, undefined>);
+    });
+
+    test('with undefined getter default', () => {
+      const getter = () => undefined;
+      expect(undefinedable(string(), getter)).toStrictEqual({
+        ...baseSchema,
+        default: getter,
+      } satisfies UndefinedableSchema<StringSchema<undefined>, typeof getter>);
+    });
+
+    test('with value default', () => {
+      expect(undefinedable(string(), 'foo')).toStrictEqual({
+        ...baseSchema,
+        default: 'foo',
+      } satisfies UndefinedableSchema<StringSchema<undefined>, 'foo'>);
+    });
+
+    test('with value getter default', () => {
+      const getter = () => 'foo';
+      expect(undefinedable(string(), getter)).toStrictEqual({
+        ...baseSchema,
+        default: getter,
+      } satisfies UndefinedableSchema<StringSchema<undefined>, typeof getter>);
+    });
+  });
+
+  describe('should return dataset without issues', () => {
+    const schema = undefinedable(string());
+
+    test('for wrapper type', () => {
+      expectNoSchemaIssue(schema, ['', 'foo', '#$%']);
+    });
+
+    test('for undefined', () => {
+      expectNoSchemaIssue(schema, [undefined]);
+    });
+  });
+
+  describe('should return dataset without default', () => {
+    const schema = undefinedable(string(), 'foo');
+
+    test('for wrapper type', () => {
+      expectNoSchemaIssue(schema, ['', 'bar', '#$%']);
+    });
+  });
+
+  describe('should return dataset with default', () => {
+    const schema1 = undefinedable(string(), undefined);
+    const schema2 = undefinedable(string(), 'foo');
+    const schema3 = undefinedable(string(), () => undefined);
+    const schema4 = undefinedable(string(), () => 'foo');
+
+    test('for undefined', () => {
+      expect(
+        schema1._run({ typed: false, value: undefined }, {})
+      ).toStrictEqual({
+        typed: true,
+        value: undefined,
+      });
+      expect(
+        schema2._run({ typed: false, value: undefined }, {})
+      ).toStrictEqual({
+        typed: true,
+        value: 'foo',
+      });
+      expect(
+        schema3._run({ typed: false, value: undefined }, {})
+      ).toStrictEqual({
+        typed: true,
+        value: undefined,
+      });
+      expect(
+        schema4._run({ typed: false, value: undefined }, {})
+      ).toStrictEqual({
+        typed: true,
+        value: 'foo',
+      });
+    });
+  });
+});
diff --git a/library/src/schemas/undefinedable/undefinedable.ts b/library/src/schemas/undefinedable/undefinedable.ts
new file mode 100644
index 000000000..129993177
--- /dev/null
+++ b/library/src/schemas/undefinedable/undefinedable.ts
@@ -0,0 +1,123 @@
+import { getDefault } from '../../methods/index.ts';
+import type {
+  BaseIssue,
+  BaseSchema,
+  Dataset,
+  Default,
+  InferInput,
+  InferIssue,
+} from '../../types/index.ts';
+import type { InferUndefinedableOutput } from './types.ts';
+
+/**
+ * Undefinedable schema type.
+ */
+export interface UndefinedableSchema<
+  TWrapped extends BaseSchema<unknown, unknown, BaseIssue<unknown>>,
+  TDefault extends Default<TWrapped, undefined>,
+> extends BaseSchema<
+    InferInput<TWrapped> | undefined,
+    InferUndefinedableOutput<TWrapped, TDefault>,
+    InferIssue<TWrapped>
+  > {
+  /**
+   * The schema type.
+   */
+  readonly type: 'undefinedable';
+  /**
+   * The schema reference.
+   */
+  readonly reference: typeof undefinedable;
+  /**
+   * The expected property.
+   */
+  readonly expects: `(${TWrapped['expects']} | undefined)`;
+  /**
+   * The wrapped schema.
+   */
+  readonly wrapped: TWrapped;
+  /**
+   * The default value.
+   */
+  readonly default: TDefault;
+}
+
+/**
+ * Creates a undefinedable schema.
+ *
+ * @param wrapped The wrapped schema.
+ *
+ * @returns A undefinedable schema.
+ */
+export function undefinedable<
+  const TWrapped extends BaseSchema<unknown, unknown, BaseIssue<unknown>>,
+>(wrapped: TWrapped): UndefinedableSchema<TWrapped, never>;
+
+/**
+ * Creates a undefinedable schema.
+ *
+ * @param wrapped The wrapped schema.
+ * @param default_ The default value.
+ *
+ * @returns A undefinedable schema.
+ */
+export function undefinedable<
+  const TWrapped extends BaseSchema<unknown, unknown, BaseIssue<unknown>>,
+  const TDefault extends Default<TWrapped, undefined>,
+>(
+  wrapped: TWrapped,
+  default_: TDefault
+): UndefinedableSchema<TWrapped, TDefault>;
+
+export function undefinedable(
+  wrapped: BaseSchema<unknown, unknown, BaseIssue<unknown>>,
+  ...args: unknown[]
+): UndefinedableSchema<
+  BaseSchema<unknown, unknown, BaseIssue<unknown>>,
+  unknown
+> {
+  // Create schema object
+  // @ts-expect-error
+  const schema: UndefinedableSchema<
+    BaseSchema<unknown, unknown, BaseIssue<unknown>>,
+    unknown
+  > = {
+    kind: 'schema',
+    type: 'undefinedable',
+    reference: undefinedable,
+    expects: `(${wrapped.expects} | undefined)`,
+    async: false,
+    wrapped,
+    _run(dataset, config) {
+      // If value is `undefined`, override it with default or return dataset
+      if (dataset.value === undefined) {
+        // If default is specified, override value of dataset
+        if ('default' in this) {
+          dataset.value = getDefault(
+            this,
+            dataset as Dataset<undefined, never>,
+            config
+          );
+        }
+
+        // If value is still `undefined`, return dataset
+        if (dataset.value === undefined) {
+          dataset.typed = true;
+          return dataset;
+        }
+      }
+
+      // Otherwise, return dataset of wrapped schema
+      return this.wrapped._run(dataset, config);
+    },
+  };
+
+  // Add default if specified
+  if (0 in args) {
+    // @ts-expect-error
+    schema.default = args[0];
+  }
+
+  // Return schema object
+  return schema;
+}
diff --git a/library/src/schemas/undefinedable/undefinedableAsync.test-d.ts b/library/src/schemas/undefinedable/undefinedableAsync.test-d.ts
new file mode 100644
index 000000000..e19393789
--- /dev/null
+++ b/library/src/schemas/undefinedable/undefinedableAsync.test-d.ts
@@ -0,0 +1,117 @@
+import { describe, expectTypeOf, test } from 'vitest';
+import type { InferInput, InferIssue, InferOutput } from '../../types/index.ts';
+import {
+  string,
+  type StringIssue,
+  type StringSchema,
+} from '../string/index.ts';
+import {
+  undefinedableAsync,
+  type UndefinedableSchemaAsync,
+} from './undefinedableAsync.ts';
+
+describe('undefinedableAsync', () => {
+  describe('should return schema object', () => {
+    test('with never default', () => {
+      expectTypeOf(undefinedableAsync(string())).toEqualTypeOf<
+        UndefinedableSchemaAsync<StringSchema<undefined>, never>
+      >();
+    });
+
+    test('with undefined default', () => {
+      expectTypeOf(undefinedableAsync(string(), undefined)).toEqualTypeOf<
+        UndefinedableSchemaAsync<StringSchema<undefined>, undefined>
+      >();
+    });
+
+    test('with undefined getter default', () => {
+      expectTypeOf(undefinedableAsync(string(), () => undefined)).toEqualTypeOf<
+        UndefinedableSchemaAsync<StringSchema<undefined>, () => undefined>
+      >();
+    });
+
+    test('with async undefined getter default', () => {
+      expectTypeOf(
+        undefinedableAsync(string(), async () => undefined)
+      ).toEqualTypeOf<
+        UndefinedableSchemaAsync<
+          StringSchema<undefined>,
+          () => Promise<undefined>
+        >
+      >();
+    });
+
+    test('with value default', () => {
+      expectTypeOf(undefinedableAsync(string(), 'foo')).toEqualTypeOf<
+        UndefinedableSchemaAsync<StringSchema<undefined>, 'foo'>
+      >();
+    });
+
+    test('with value getter default', () => {
+      expectTypeOf(undefinedableAsync(string(), () => 'foo')).toEqualTypeOf<
+        UndefinedableSchemaAsync<StringSchema<undefined>, () => string>
+      >();
+    });
+
+    test('with async value getter default', () => {
+      expectTypeOf(
+        undefinedableAsync(string(), async () => 'foo')
+      ).toEqualTypeOf<
+        UndefinedableSchemaAsync<StringSchema<undefined>, () => Promise<string>>
+      >();
+    });
+  });
+
+  describe('should infer correct types', () => {
+    type Schema1 = UndefinedableSchemaAsync<StringSchema<undefined>, never>;
+    type Schema2 = UndefinedableSchemaAsync<StringSchema<undefined>, undefined>;
+    type Schema3 = UndefinedableSchemaAsync<StringSchema<undefined>, 'foo'>;
+    type Schema4 = UndefinedableSchemaAsync<
+      StringSchema<undefined>,
+      () => undefined
+    >;
+    type Schema5 = UndefinedableSchemaAsync<
+      StringSchema<undefined>,
+      () => 'foo'
+    >;
+    type Schema6 = UndefinedableSchemaAsync<
+      StringSchema<undefined>,
+      () => Promise<undefined>
+    >;
+    type Schema7 = UndefinedableSchemaAsync<
+      StringSchema<undefined>,
+      () => Promise<'foo'>
+    >;
+
+    test('of input', () => {
+      type Input = string | undefined;
+      expectTypeOf<InferInput<Schema1>>().toEqualTypeOf<Input>();
+      expectTypeOf<InferInput<Schema2>>().toEqualTypeOf<Input>();
+      expectTypeOf<InferInput<Schema3>>().toEqualTypeOf<Input>();
+      expectTypeOf<InferInput<Schema4>>().toEqualTypeOf<Input>();
+      expectTypeOf<InferInput<Schema5>>().toEqualTypeOf<Input>();
+      expectTypeOf<InferInput<Schema6>>().toEqualTypeOf<Input>();
+      expectTypeOf<InferInput<Schema7>>().toEqualTypeOf<Input>();
+    });
+
+    test('of output', () => {
+      expectTypeOf<InferOutput<Schema1>>().toEqualTypeOf<string | undefined>();
+      expectTypeOf<InferOutput<Schema2>>().toEqualTypeOf<string | undefined>();
+      expectTypeOf<InferOutput<Schema3>>().toEqualTypeOf<string>();
+      expectTypeOf<InferOutput<Schema4>>().toEqualTypeOf<string | undefined>();
+      expectTypeOf<InferOutput<Schema5>>().toEqualTypeOf<string>();
+      expectTypeOf<InferOutput<Schema6>>().toEqualTypeOf<string | undefined>();
+      expectTypeOf<InferOutput<Schema7>>().toEqualTypeOf<string>();
+    });
+
+    test('of issue', () => {
+      expectTypeOf<InferIssue<Schema1>>().toEqualTypeOf<StringIssue>();
+      expectTypeOf<InferIssue<Schema2>>().toEqualTypeOf<StringIssue>();
+      expectTypeOf<InferIssue<Schema3>>().toEqualTypeOf<StringIssue>();
+      expectTypeOf<InferIssue<Schema4>>().toEqualTypeOf<StringIssue>();
+      expectTypeOf<InferIssue<Schema5>>().toEqualTypeOf<StringIssue>();
+      expectTypeOf<InferIssue<Schema6>>().toEqualTypeOf<StringIssue>();
+      expectTypeOf<InferIssue<Schema7>>().toEqualTypeOf<StringIssue>();
+    });
+  });
+});
diff --git a/library/src/schemas/undefinedable/undefinedableAsync.test.ts b/library/src/schemas/undefinedable/undefinedableAsync.test.ts
new file mode 100644
index 000000000..61daa0afc
--- /dev/null
+++ b/library/src/schemas/undefinedable/undefinedableAsync.test.ts
@@ -0,0 +1,154 @@
+import { describe, expect, test } from 'vitest';
+import { expectNoSchemaIssueAsync } from '../../vitest/index.ts';
+import { string, type StringSchema } from '../string/index.ts';
+import {
+  undefinedableAsync,
+  type UndefinedableSchemaAsync,
+} from './undefinedableAsync.ts';
+
+describe('undefinedableAsync', () => {
+  describe('should return schema object', () => {
+    const baseSchema: Omit<
+      UndefinedableSchemaAsync<StringSchema<undefined>, string>,
+      'default'
+    > = {
+      kind: 'schema',
+      type: 'undefinedable',
+      reference: undefinedableAsync,
+      expects: '(string | undefined)',
+      wrapped: { ...string(), _run: expect.any(Function) },
+      async: true,
+      _run: expect.any(Function),
+    };
+
+    test('with never default', () => {
+      expect(undefinedableAsync(string())).toStrictEqual(baseSchema);
+    });
+
+    test('with undefined default', () => {
+      expect(undefinedableAsync(string(), undefined)).toStrictEqual({
+        ...baseSchema,
+        default: undefined,
+      } satisfies UndefinedableSchemaAsync<StringSchema<undefined>, undefined>);
+    });
+
+    test('with undefined getter default', () => {
+      const getter = () => undefined;
+      expect(undefinedableAsync(string(), getter)).toStrictEqual({
+        ...baseSchema,
+        default: getter,
+      } satisfies UndefinedableSchemaAsync<
+        StringSchema<undefined>,
+        typeof getter
+      >);
+    });
+
+    test('with async undefined getter default', () => {
+      const getter = async () => undefined;
+      expect(undefinedableAsync(string(), getter)).toStrictEqual({
+        ...baseSchema,
+        default: getter,
+      } satisfies UndefinedableSchemaAsync<
+        StringSchema<undefined>,
+        typeof getter
+      >);
+    });
+
+    test('with value default', () => {
+      expect(undefinedableAsync(string(), 'foo')).toStrictEqual({
+        ...baseSchema,
+        default: 'foo',
+      } satisfies UndefinedableSchemaAsync<StringSchema<undefined>, 'foo'>);
+    });
+
+    test('with value getter default', () => {
+      const getter = () => 'foo';
+      expect(undefinedableAsync(string(), getter)).toStrictEqual({
+        ...baseSchema,
+        default: getter,
+      } satisfies UndefinedableSchemaAsync<
+        StringSchema<undefined>,
+        typeof getter
+      >);
+    });
+
+    test('with async value getter default', () => {
+      const getter = async () => 'foo';
+      expect(undefinedableAsync(string(), getter)).toStrictEqual({
+        ...baseSchema,
+        default: getter,
+      } satisfies UndefinedableSchemaAsync<
+        StringSchema<undefined>,
+        typeof getter
+      >);
+    });
+  });
+
+  describe('should return dataset without issues', () => {
+    const schema = undefinedableAsync(string());
+
+    test('for wrapper type', async () => {
+      await expectNoSchemaIssueAsync(schema, ['', 'foo', '#$%']);
+    });
+
+    test('for undefined', async () => {
+      await expectNoSchemaIssueAsync(schema, [undefined]);
+    });
+  });
+
+  describe('should return dataset without default', () => {
+    const schema = undefinedableAsync(string(), 'foo');
+
+    test('for wrapper type', async () => {
+      await expectNoSchemaIssueAsync(schema, ['', 'bar', '#$%']);
+    });
+  });
+
+  describe('should return dataset with default', () => {
+    const schema1 = undefinedableAsync(string(), undefined);
+    const schema2 = undefinedableAsync(string(), 'foo');
+    const schema3 = undefinedableAsync(string(), () => undefined);
+    const schema4 = undefinedableAsync(string(), () => 'foo');
+    const schema5 = undefinedableAsync(string(), async () => undefined);
+    const schema6 = undefinedableAsync(string(), async () => 'foo');
+
+    test('for undefined', async () => {
+      expect(
+        await schema1._run({ typed: false, value: undefined }, {})
+      ).toStrictEqual({
+        typed: true,
+        value: undefined,
+      });
+      expect(
+        await schema2._run({ typed: false, value: undefined }, {})
+      ).toStrictEqual({
+        typed: true,
+        value: 'foo',
+      });
+      expect(
+        await schema3._run({ typed: false, value: undefined }, {})
+      ).toStrictEqual({
+        typed: true,
+        value: undefined,
+      });
+      expect(
+        await schema4._run({ typed: false, value: undefined }, {})
+      ).toStrictEqual({
+        typed: true,
+        value: 'foo',
+      });
+      expect(
+        await schema5._run({ typed: false, value: undefined }, {})
+      ).toStrictEqual({
+        typed: true,
+        value: undefined,
+      });
+      expect(
+        await schema6._run({ typed: false, value: undefined }, {})
+      ).toStrictEqual({
+        typed: true,
+        value: 'foo',
+      });
+    });
+  });
+});
diff --git a/library/src/schemas/undefinedable/undefinedableAsync.ts b/library/src/schemas/undefinedable/undefinedableAsync.ts
new file mode 100644
index 000000000..63d716886
--- /dev/null
+++ b/library/src/schemas/undefinedable/undefinedableAsync.ts
@@ -0,0 +1,134 @@
+import { getDefault } from '../../methods/index.ts';
+import type {
+  BaseIssue,
+  BaseSchema,
+  BaseSchemaAsync,
+  Dataset,
+  DefaultAsync,
+  InferInput,
+  InferIssue,
+} from '../../types/index.ts';
+import type { InferUndefinedableOutput } from './types.ts';
+
+/**
+ * Undefinedable schema async type.
+ */
+export interface UndefinedableSchemaAsync<
+  TWrapped extends
+    | BaseSchema<unknown, unknown, BaseIssue<unknown>>
+    | BaseSchemaAsync<unknown, unknown, BaseIssue<unknown>>,
+  TDefault extends DefaultAsync<TWrapped, undefined>,
+> extends BaseSchemaAsync<
+    InferInput<TWrapped> | undefined,
+    InferUndefinedableOutput<TWrapped, TDefault>,
+    InferIssue<TWrapped>
+  > {
+  /**
+   * The schema type.
+   */
+  readonly type: 'undefinedable';
+  /**
+   * The schema reference.
+   */
+  readonly reference: typeof undefinedableAsync;
+  /**
+   * The expected property.
+   */
+  readonly expects: `(${TWrapped['expects']} | undefined)`;
+  /**
+   * The wrapped schema.
+   */
+  readonly wrapped: TWrapped;
+  /**
+   * The default value.
+   */
+  readonly default: TDefault;
+}
+
+/**
+ * Creates an undefinedable schema.
+ *
+ * @param wrapped The wrapped schema.
+ *
+ * @returns An undefinedable schema.
+ */
+export function undefinedableAsync<
+  const TWrapped extends
+    | BaseSchema<unknown, unknown, BaseIssue<unknown>>
+    | BaseSchemaAsync<unknown, unknown, BaseIssue<unknown>>,
+>(wrapped: TWrapped): UndefinedableSchemaAsync<TWrapped, never>;
+
+/**
+ * Creates an undefinedable schema.
+ *
+ * @param wrapped The wrapped schema.
+ * @param default_ The default value.
+ *
+ * @returns An undefinedable schema.
+ */
+export function undefinedableAsync<
+  const TWrapped extends
+    | BaseSchema<unknown, unknown, BaseIssue<unknown>>
+    | BaseSchemaAsync<unknown, unknown, BaseIssue<unknown>>,
+  const TDefault extends DefaultAsync<TWrapped, undefined>,
+>(
+  wrapped: TWrapped,
+  default_: TDefault
+): UndefinedableSchemaAsync<TWrapped, TDefault>;
+
+export function undefinedableAsync(
+  wrapped:
+    | BaseSchema<unknown, unknown, BaseIssue<unknown>>
+    | BaseSchemaAsync<unknown, unknown, BaseIssue<unknown>>,
+  ...args: unknown[]
+): UndefinedableSchemaAsync<
+  | BaseSchema<unknown, unknown, BaseIssue<unknown>>
+  | BaseSchemaAsync<unknown, unknown, BaseIssue<unknown>>,
+  unknown
+> {
+  // Create schema object
+  // @ts-expect-error
+  const schema: UndefinedableSchemaAsync<
+    | BaseSchema<unknown, unknown, BaseIssue<unknown>>
+    | BaseSchemaAsync<unknown, unknown, BaseIssue<unknown>>,
+    unknown
+  > = {
+    kind: 'schema',
+    type: 'undefinedable',
+    reference: undefinedableAsync,
+    expects: `(${wrapped.expects} | undefined)`,
+    async: true,
+    wrapped,
+    async _run(dataset, config) {
+      // If value is `undefined`, override it with default or return dataset
+      if (dataset.value === undefined) {
+        // If default is specified, override value of dataset
+        if ('default' in this) {
+          dataset.value = await getDefault(
+            this,
+            dataset as Dataset<undefined, never>,
+            config
+          );
+        }
+
+        // If value is still `undefined`, return dataset
+        if (dataset.value === undefined) {
+          dataset.typed = true;
+          return dataset;
+        }
+      }
+
+      // Otherwise, return dataset of wrapped schema
+      return this.wrapped._run(dataset, config);
+    },
+  };
+
+  // Add default if specified
+  if (0 in args) {
+    // @ts-expect-error
+    schema.default = args[0];
+  }
+
+  // Return schema object
+  return schema;
+}
diff --git a/library/src/types/issue.ts b/library/src/types/issue.ts
index 11e439ddb..98707f043 100644
--- a/library/src/types/issue.ts
+++ b/library/src/types/issue.ts
@@ -56,6 +56,8 @@ import type {
   TupleWithRestIssue,
   TupleWithRestSchema,
   TupleWithRestSchemaAsync,
+  UndefinedableSchema,
+  UndefinedableSchemaAsync,
   UnionIssue,
   UnionSchema,
   UnionSchemaAsync,
@@ -571,6 +573,33 @@ export type IssueDotPath<
                                 undefined
                               >
                             >
+                          | UndefinedableSchema<
+                              infer TWrapped,
+                              Default<
+                                BaseSchema<
+                                  unknown,
+                                  unknown,
+                                  BaseIssue<unknown>
+                                >,
+                                undefined
+                              >
+                            >
+                          | UndefinedableSchemaAsync<
+                              infer TWrapped,
+                              DefaultAsync<
+                                | BaseSchema<
+                                    unknown,
+                                    unknown,
+                                    BaseIssue<unknown>
+                                  >
+                                | BaseSchemaAsync<
+                                    unknown,
+                                    unknown,
+                                    BaseIssue<unknown>
+                                  >,
+                                undefined
+                              >
+                            >
                       ? IssueDotPath<TWrapped>
                       : // Otherwise
                         never;
diff --git a/library/src/types/object.ts b/library/src/types/object.ts
index 6bccc17ab..17c66d123 100644
--- a/library/src/types/object.ts
+++ b/library/src/types/object.ts
@@ -117,14 +117,10 @@ type ExactOptionalInput<
     | BaseSchema<unknown, unknown, BaseIssue<unknown>>
     | BaseSchemaAsync<unknown, unknown, BaseIssue<unknown>>,
 > = TSchema extends
-  | NullishSchema<infer TWrapped, never>
-  | NullishSchemaAsync<infer TWrapped, never>
-  ? ExactOptionalInput<TWrapped> | null
-  : TSchema extends
-        | OptionalSchema<infer TWrapped, never>
-        | OptionalSchemaAsync<infer TWrapped, never>
-    ? ExactOptionalInput<TWrapped>
-    : InferInput<TSchema>;
+  | OptionalSchema<infer TWrapped, never>
+  | OptionalSchemaAsync<infer TWrapped, never>
+  ? ExactOptionalInput<TWrapped>
+  : InferInput<TSchema>;
 
 /**
  * Exact optional output type.
@@ -134,18 +130,12 @@ type ExactOptionalOutput<
     | BaseSchema<unknown, unknown, BaseIssue<unknown>>
     | BaseSchemaAsync<unknown, unknown, BaseIssue<unknown>>,
 > = TSchema extends
-  | NullishSchema<infer TWrapped, never>
-  | NullishSchemaAsync<infer TWrapped, never>
+  | OptionalSchema<infer TWrapped, never>
+  | OptionalSchemaAsync<infer TWrapped, never>
   ? HasDefault<TSchema> extends true
     ? InferOutput<TSchema>
-    : ExactOptionalOutput<TWrapped> | null
-  : TSchema extends
-        | OptionalSchema<infer TWrapped, never>
-        | OptionalSchemaAsync<infer TWrapped, never>
-    ? HasDefault<TSchema> extends true
-      ? InferOutput<TSchema>
-      : ExactOptionalOutput<TWrapped>
-    : InferOutput<TSchema>;
+    : ExactOptionalOutput<TWrapped>
+  : InferOutput<TSchema>;
 
 /**
  * Infer entries input type.
diff --git a/website/src/routes/api/(actions)/brand/index.mdx b/website/src/routes/api/(actions)/brand/index.mdx
index 6f3b15ca9..e6619bd7d 100644
--- a/website/src/routes/api/(actions)/brand/index.mdx
+++ b/website/src/routes/api/(actions)/brand/index.mdx
@@ -102,6 +102,7 @@ The following APIs can be combined with `brand`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(actions)/check/index.mdx b/website/src/routes/api/(actions)/check/index.mdx
index c7d621058..22e910ba2 100644
--- a/website/src/routes/api/(actions)/check/index.mdx
+++ b/website/src/routes/api/(actions)/check/index.mdx
@@ -104,6 +104,7 @@ The following APIs can be combined with `check`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(actions)/description/index.mdx b/website/src/routes/api/(actions)/description/index.mdx
index 93488a1da..84226179f 100644
--- a/website/src/routes/api/(actions)/description/index.mdx
+++ b/website/src/routes/api/(actions)/description/index.mdx
@@ -100,6 +100,7 @@ The following APIs can be combined with `description`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(actions)/rawCheck/index.mdx b/website/src/routes/api/(actions)/rawCheck/index.mdx
index c08bd59a8..c05691af5 100644
--- a/website/src/routes/api/(actions)/rawCheck/index.mdx
+++ b/website/src/routes/api/(actions)/rawCheck/index.mdx
@@ -127,6 +127,7 @@ The following APIs can be combined with `rawCheck`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(actions)/rawTransform/index.mdx b/website/src/routes/api/(actions)/rawTransform/index.mdx
index cd7ff7ae4..8716748ba 100644
--- a/website/src/routes/api/(actions)/rawTransform/index.mdx
+++ b/website/src/routes/api/(actions)/rawTransform/index.mdx
@@ -145,6 +145,7 @@ The following APIs can be combined with `rawTransform`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(actions)/readonly/index.mdx b/website/src/routes/api/(actions)/readonly/index.mdx
index 6883f8b3b..e3d88b970 100644
--- a/website/src/routes/api/(actions)/readonly/index.mdx
+++ b/website/src/routes/api/(actions)/readonly/index.mdx
@@ -97,6 +97,7 @@ The following APIs can be combined with `readonly`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(actions)/transform/index.mdx b/website/src/routes/api/(actions)/transform/index.mdx
index bb880b5d3..76f7870d0 100644
--- a/website/src/routes/api/(actions)/transform/index.mdx
+++ b/website/src/routes/api/(actions)/transform/index.mdx
@@ -113,6 +113,7 @@ The following APIs can be combined with `transform`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(async)/arrayAsync/index.mdx b/website/src/routes/api/(async)/arrayAsync/index.mdx
index dd32259c3..7411220bb 100644
--- a/website/src/routes/api/(async)/arrayAsync/index.mdx
+++ b/website/src/routes/api/(async)/arrayAsync/index.mdx
@@ -106,6 +106,7 @@ The following APIs can be combined with `arrayAsync`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(async)/awaitAsync/index.mdx b/website/src/routes/api/(async)/awaitAsync/index.mdx
index 99fb3a7f8..20c28bdc8 100644
--- a/website/src/routes/api/(async)/awaitAsync/index.mdx
+++ b/website/src/routes/api/(async)/awaitAsync/index.mdx
@@ -94,6 +94,7 @@ The following APIs can be combined with `awaitAsync`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(async)/checkAsync/index.mdx b/website/src/routes/api/(async)/checkAsync/index.mdx
index c20227322..6f2ec87e0 100644
--- a/website/src/routes/api/(async)/checkAsync/index.mdx
+++ b/website/src/routes/api/(async)/checkAsync/index.mdx
@@ -107,6 +107,7 @@ The following APIs can be combined with `checkAsync`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(async)/customAsync/index.mdx b/website/src/routes/api/(async)/customAsync/index.mdx
index fef6cf184..5d0acfb14 100644
--- a/website/src/routes/api/(async)/customAsync/index.mdx
+++ b/website/src/routes/api/(async)/customAsync/index.mdx
@@ -94,6 +94,7 @@ The following APIs can be combined with `customAsync`.
     'strictTuple',
     'tuple',
     'tupleWithRest',
+    'undefinedable',
     'union',
   ]}
 />
diff --git a/website/src/routes/api/(async)/fallbackAsync/index.mdx b/website/src/routes/api/(async)/fallbackAsync/index.mdx
index ec88d4a6f..d8602b874 100644
--- a/website/src/routes/api/(async)/fallbackAsync/index.mdx
+++ b/website/src/routes/api/(async)/fallbackAsync/index.mdx
@@ -108,6 +108,7 @@ The following APIs can be combined with `fallbackAsync`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(async)/getDefaultsAsync/index.mdx b/website/src/routes/api/(async)/getDefaultsAsync/index.mdx
index 70bf4c35f..fef72a777 100644
--- a/website/src/routes/api/(async)/getDefaultsAsync/index.mdx
+++ b/website/src/routes/api/(async)/getDefaultsAsync/index.mdx
@@ -111,6 +111,7 @@ The following APIs can be combined with `getDefaultsAsync`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(async)/getFallbacksAsync/index.mdx b/website/src/routes/api/(async)/getFallbacksAsync/index.mdx
index 2d60fb9ee..5221da09e 100644
--- a/website/src/routes/api/(async)/getFallbacksAsync/index.mdx
+++ b/website/src/routes/api/(async)/getFallbacksAsync/index.mdx
@@ -109,6 +109,7 @@ The following APIs can be combined with `getFallbacksAsync`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(async)/intersectAsync/index.mdx b/website/src/routes/api/(async)/intersectAsync/index.mdx
index 5e941ae92..60a86e02b 100644
--- a/website/src/routes/api/(async)/intersectAsync/index.mdx
+++ b/website/src/routes/api/(async)/intersectAsync/index.mdx
@@ -121,6 +121,7 @@ The following APIs can be combined with `intersectAsync`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(async)/lazyAsync/index.mdx b/website/src/routes/api/(async)/lazyAsync/index.mdx
index 0769706dc..b1e791efc 100644
--- a/website/src/routes/api/(async)/lazyAsync/index.mdx
+++ b/website/src/routes/api/(async)/lazyAsync/index.mdx
@@ -151,9 +151,10 @@ The following APIs can be combined with `lazyAsync`.
     'string',
     'symbol',
     'tuple',
+    'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
-    'unionWithRest',
     'unknown',
     'variant',
     'void',
diff --git a/website/src/routes/api/(async)/looseObjectAsync/index.mdx b/website/src/routes/api/(async)/looseObjectAsync/index.mdx
index e1192b7e9..7b48577ea 100644
--- a/website/src/routes/api/(async)/looseObjectAsync/index.mdx
+++ b/website/src/routes/api/(async)/looseObjectAsync/index.mdx
@@ -113,6 +113,7 @@ The following APIs can be combined with `looseObjectAsync`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(async)/looseTupleAsync/index.mdx b/website/src/routes/api/(async)/looseTupleAsync/index.mdx
index a979b1756..edf16df29 100644
--- a/website/src/routes/api/(async)/looseTupleAsync/index.mdx
+++ b/website/src/routes/api/(async)/looseTupleAsync/index.mdx
@@ -107,6 +107,7 @@ The following APIs can be combined with `looseTupleAsync`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(async)/mapAsync/index.mdx b/website/src/routes/api/(async)/mapAsync/index.mdx
index 2b37d5fa3..3674a25f6 100644
--- a/website/src/routes/api/(async)/mapAsync/index.mdx
+++ b/website/src/routes/api/(async)/mapAsync/index.mdx
@@ -105,6 +105,7 @@ The following APIs can be combined with `mapAsync`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(async)/nonNullableAsync/index.mdx b/website/src/routes/api/(async)/nonNullableAsync/index.mdx
index 7208d86b9..6d98168a3 100644
--- a/website/src/routes/api/(async)/nonNullableAsync/index.mdx
+++ b/website/src/routes/api/(async)/nonNullableAsync/index.mdx
@@ -110,6 +110,7 @@ The following APIs can be combined with `nonNullableAsync`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(async)/nonNullishAsync/index.mdx b/website/src/routes/api/(async)/nonNullishAsync/index.mdx
index 66fc514c6..1ed36b2d6 100644
--- a/website/src/routes/api/(async)/nonNullishAsync/index.mdx
+++ b/website/src/routes/api/(async)/nonNullishAsync/index.mdx
@@ -106,6 +106,7 @@ The following APIs can be combined with `nonNullishAsync`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(async)/nonOptionalAsync/index.mdx b/website/src/routes/api/(async)/nonOptionalAsync/index.mdx
index c42fb1a44..7bf3ef3be 100644
--- a/website/src/routes/api/(async)/nonOptionalAsync/index.mdx
+++ b/website/src/routes/api/(async)/nonOptionalAsync/index.mdx
@@ -116,6 +116,7 @@ The following APIs can be combined with `nonOptionalAsync`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(async)/objectAsync/index.mdx b/website/src/routes/api/(async)/objectAsync/index.mdx
index 7579b7c4f..c0da376d0 100644
--- a/website/src/routes/api/(async)/objectAsync/index.mdx
+++ b/website/src/routes/api/(async)/objectAsync/index.mdx
@@ -113,6 +113,7 @@ The following APIs can be combined with `objectAsync`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(async)/objectWithRestAsync/index.mdx b/website/src/routes/api/(async)/objectWithRestAsync/index.mdx
index a73652afe..d07c1b371 100644
--- a/website/src/routes/api/(async)/objectWithRestAsync/index.mdx
+++ b/website/src/routes/api/(async)/objectWithRestAsync/index.mdx
@@ -127,6 +127,7 @@ The following APIs can be combined with `objectWithRestAsync`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(async)/parseAsync/index.mdx b/website/src/routes/api/(async)/parseAsync/index.mdx
index bf798f77e..d432742b0 100644
--- a/website/src/routes/api/(async)/parseAsync/index.mdx
+++ b/website/src/routes/api/(async)/parseAsync/index.mdx
@@ -108,6 +108,7 @@ The following APIs can be combined with `parseAsync`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(async)/parserAsync/index.mdx b/website/src/routes/api/(async)/parserAsync/index.mdx
index a738a07f6..723de006b 100644
--- a/website/src/routes/api/(async)/parserAsync/index.mdx
+++ b/website/src/routes/api/(async)/parserAsync/index.mdx
@@ -102,6 +102,7 @@ The following APIs can be combined with `parserAsync`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(async)/safeParseAsync/index.mdx b/website/src/routes/api/(async)/safeParseAsync/index.mdx
index 754be47e0..87e444d72 100644
--- a/website/src/routes/api/(async)/safeParseAsync/index.mdx
+++ b/website/src/routes/api/(async)/safeParseAsync/index.mdx
@@ -1,10 +1,165 @@
 ---
 title: safeParseAsync
+description: Parses an unknown input based on a schema.
 source: /methods/safeParse/safeParseAsync.ts
 contributors:
   - fabian-hiller
+  - EltonLobo07
 ---
 
+import { ApiList, Property } from '~/components';
+import { properties } from './properties';
+
 # safeParseAsync
 
-> The content of this page is not yet ready. Until then, please use the [source code](https://github.com/fabian-hiller/valibot/blob/main/library/src/methods/safeParse/safeParseAsync.ts) or take a look at [issue #287](https://github.com/fabian-hiller/valibot/issues/287) to help us extend the API reference.
+Parses an unknown input based on a schema.
+
+```ts
+const result = v.safeParseAsync<TSchema>(schema, input, config);
+```
+
+## Generics
+
+- `TSchema` <Property {...properties.TSchema} />
+
+## Parameters
+
+- `schema` <Property {...properties.schema} />
+- `input` <Property {...properties.input} />
+- `config` <Property {...properties.config} />
+
+## Returns
+
+- `result` <Property {...properties.result} />
+
+## Example
+
+The following example shows how `safeParseAsync` can be used.
+
+```ts
+import { isEmailPresent } from '~/api';
+
+const StoredEmailSchema = v.pipeAsync(
+  v.string(),
+  v.email(),
+  v.checkAsync(isEmailPresent, 'The email is not in the database.')
+);
+const result = await v.safeParseAsync(StoredEmailSchema, 'jane@example.com');
+
+if (result.success) {
+  const storedEmail = result.output;
+} else {
+  console.error(result.issues);
+}
+```
+
+## Related
+
+The following APIs can be combined with `safeParseAsync`.
+
+### Schemas
+
+<ApiList
+  items={[
+    'any',
+    'array',
+    'bigint',
+    'blob',
+    'boolean',
+    'custom',
+    'date',
+    'enum',
+    'file',
+    'function',
+    'instance',
+    'intersect',
+    'lazy',
+    'literal',
+    'looseObject',
+    'looseTuple',
+    'map',
+    'nan',
+    'never',
+    'nonNullable',
+    'nonNullish',
+    'nonOptional',
+    'null',
+    'nullable',
+    'nullish',
+    'number',
+    'object',
+    'objectWithRest',
+    'optional',
+    'picklist',
+    'promise',
+    'record',
+    'set',
+    'strictObject',
+    'strictTuple',
+    'string',
+    'symbol',
+    'tuple',
+    'tupleWithRest',
+    'undefined',
+    'undefinedable',
+    'union',
+    'unknown',
+    'variant',
+    'void',
+  ]}
+/>
+
+### Methods
+
+<ApiList
+  items={[
+    'config',
+    'fallback',
+    'flatten',
+    'keyof',
+    'omit',
+    'partial',
+    'pick',
+    'pipe',
+    'required',
+    'unwrap',
+  ]}
+/>
+
+### Utils
+
+<ApiList items={['getDotPath']} />
+
+### Async
+
+<ApiList
+  items={[
+    'arrayAsync',
+    'customAsync',
+    'fallbackAsync',
+    'intersectAsync',
+    'lazyAsync',
+    'looseObjectAsync',
+    'looseTupleAsync',
+    'mapAsync',
+    'nonNullableAsync',
+    'nonNullishAsync',
+    'nonOptionalAsync',
+    'nullableAsync',
+    'nullishAsync',
+    'objectAsync',
+    'objectWithRestAsync',
+    'optionalAsync',
+    'partialAsync',
+    'pipeAsync',
+    'recordAsync',
+    'requiredAsync',
+    'setAsync',
+    'strictObjectAsync',
+    'strictTupleAsync',
+    'tupleAsync',
+    'tupleWithRestAsync',
+    'unionAsync',
+    'variantAsync',
+  ]}
+/>
diff --git a/website/src/routes/api/(async)/safeParseAsync/properties.ts b/website/src/routes/api/(async)/safeParseAsync/properties.ts
new file mode 100644
index 000000000..516deb2b1
--- /dev/null
+++ b/website/src/routes/api/(async)/safeParseAsync/properties.ts
@@ -0,0 +1,96 @@
+import type { PropertyProps } from '~/components';
+
+export const properties: Record<string, PropertyProps> = {
+  TSchema: {
+    modifier: 'extends',
+    type: {
+      type: 'union',
+      options: [
+        {
+          type: 'custom',
+          name: 'BaseSchema',
+          href: '../BaseSchema/',
+          generics: [
+            'unknown',
+            'unknown',
+            {
+              type: 'custom',
+              name: 'BaseIssue',
+              href: '../BaseIssue/',
+              generics: ['unknown'],
+            },
+          ],
+        },
+        {
+          type: 'custom',
+          name: 'BaseSchemaAsync',
+          href: '../BaseSchemaAsync/',
+          generics: [
+            'unknown',
+            'unknown',
+            {
+              type: 'custom',
+              name: 'BaseIssue',
+              href: '../BaseIssue/',
+              generics: ['unknown'],
+            },
+          ],
+        },
+      ],
+    },
+  },
+  schema: {
+    type: {
+      type: 'custom',
+      name: 'TSchema',
+    },
+  },
+  input: {
+    type: 'unknown',
+  },
+  config: {
+    type: {
+      type: 'union',
+      options: [
+        {
+          type: 'custom',
+          name: 'Config',
+          href: '../Config/',
+          generics: [
+            {
+              type: 'custom',
+              name: 'InferIssue',
+              href: '../InferIssue/',
+              generics: [
+                {
+                  type: 'custom',
+                  name: 'TSchema',
+                },
+              ],
+            },
+          ],
+        },
+        'undefined',
+      ],
+    },
+  },
+  result: {
+    type: {
+      type: 'custom',
+      name: 'Promise',
+      generics: [
+        {
+          type: 'custom',
+          name: 'SafeParseResult',
+          href: '../SafeParseResult/',
+          generics: [
+            {
+              type: 'custom',
+              name: 'TSchema',
+            },
+          ],
+        },
+      ],
+    },
+  },
+};
diff --git a/website/src/routes/api/(async)/setAsync/index.mdx b/website/src/routes/api/(async)/setAsync/index.mdx
index e848da89d..bd54032bb 100644
--- a/website/src/routes/api/(async)/setAsync/index.mdx
+++ b/website/src/routes/api/(async)/setAsync/index.mdx
@@ -103,6 +103,7 @@ The following APIs can be combined with `setAsync`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(async)/strictObjectAsync/index.mdx b/website/src/routes/api/(async)/strictObjectAsync/index.mdx
index 02c5b08f7..0584b0c0f 100644
--- a/website/src/routes/api/(async)/strictObjectAsync/index.mdx
+++ b/website/src/routes/api/(async)/strictObjectAsync/index.mdx
@@ -113,6 +113,7 @@ The following APIs can be combined with `strictObjectAsync`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(async)/strictTupleAsync/index.mdx b/website/src/routes/api/(async)/strictTupleAsync/index.mdx
index 566aee2b7..01715affd 100644
--- a/website/src/routes/api/(async)/strictTupleAsync/index.mdx
+++ b/website/src/routes/api/(async)/strictTupleAsync/index.mdx
@@ -107,6 +107,7 @@ The following APIs can be combined with `strictTupleAsync`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(async)/tupleAsync/index.mdx b/website/src/routes/api/(async)/tupleAsync/index.mdx
index 1d0230276..e8bff9e0a 100644
--- a/website/src/routes/api/(async)/tupleAsync/index.mdx
+++ b/website/src/routes/api/(async)/tupleAsync/index.mdx
@@ -107,6 +107,7 @@ The following APIs can be combined with `tupleAsync`.
     'symbol',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(async)/tupleWithRestAsync/index.mdx b/website/src/routes/api/(async)/tupleWithRestAsync/index.mdx
index 1c644a6a7..743534ac7 100644
--- a/website/src/routes/api/(async)/tupleWithRestAsync/index.mdx
+++ b/website/src/routes/api/(async)/tupleWithRestAsync/index.mdx
@@ -114,6 +114,7 @@ The following APIs can be combined with `tupleWithRestAsync`.
     'symbol',
     'tuple',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(async)/undefinedableAsync/index.mdx b/website/src/routes/api/(async)/undefinedableAsync/index.mdx
new file mode 100644
index 000000000..2152a8594
--- /dev/null
+++ b/website/src/routes/api/(async)/undefinedableAsync/index.mdx
@@ -0,0 +1,10 @@
+---
+title: undefinedableAsync
+source: /schemas/undefinedable/undefinedableAsync.ts
+contributors:
+  - fabian-hiller
+---
+
+# undefinedableAsync
+
+> The content of this page is not yet ready. Until then, please use the [source code](https://github.com/fabian-hiller/valibot/blob/main/library/src/schemas/undefinedable/undefinedableAsync.ts) or take a look at [issue #287](https://github.com/fabian-hiller/valibot/issues/287) to help us extend the API reference.
diff --git a/website/src/routes/api/(async)/unionAsync/index.mdx b/website/src/routes/api/(async)/unionAsync/index.mdx
index 2e30ee54b..e9c89be1b 100644
--- a/website/src/routes/api/(async)/unionAsync/index.mdx
+++ b/website/src/routes/api/(async)/unionAsync/index.mdx
@@ -1,10 +1,258 @@
 ---
 title: unionAsync
+description: Creates an union schema.
 source: /schemas/union/unionAsync.ts
 contributors:
   - fabian-hiller
+  - EltonLobo07
 ---
 
+import { Link } from '@builder.io/qwik-city';
+import { ApiList, Property } from '~/components';
+import { properties } from './properties';
+
 # unionAsync
 
-> The content of this page is not yet ready. Until then, please use the [source code](https://github.com/fabian-hiller/valibot/blob/main/library/src/schemas/union/unionAsync.ts) or take a look at [issue #287](https://github.com/fabian-hiller/valibot/issues/287) to help us extend the API reference.
+Creates an union schema.
+
+> I recommend that you read the <Link href="/guides/unions/">unions guide</Link> before using this schema function.
+
+```ts
+const Schema = v.unionAsync<TOptions, TMessage>(options, message);
+```
+
+## Generics
+
+- `TOptions` <Property {...properties.TOptions} />
+- `TMessage` <Property {...properties.TMessage} />
+
+## Parameters
+
+- `options` <Property {...properties.options} />
+- `message` <Property {...properties.message} />
+
+### Explanation
+
+With `unionAsync` you can validate if the input matches one of the given `options`. If the input does not match a schema and cannot be clearly assigned to one of the options, you can use `message` to customize the error message.
+
+If a bad input can be uniquely assigned to one of the schemas based on the data type, the result of that schema is returned. Otherwise, a general issue is returned that contains the issues of each schema as subissues. This is a special case within the library, as the issues of `unionAsync` can contradict each other.
+
+## Returns
+
+- `Schema` <Property {...properties.Schema} />
+
+## Examples
+
+The following examples show how `unionAsync` can be used.
+
+### User schema
+
+Schema to validate a user's email or username.
+
+```ts
+import { isEmailPresent, isUsernamePresent } from '~/api';
+
+const UserSchema = v.unionAsync([
+  v.pipeAsync(
+    v.string(),
+    v.email(),
+    v.checkAsync(isEmailPresent, 'The email is not in the database.')
+  ),
+  v.pipeAsync(
+    v.string(),
+    v.nonEmpty(),
+    v.checkAsync(isUsernamePresent, 'The username is not in the database.')
+  ),
+]);
+```
+
+## Related
+
+The following APIs can be combined with `unionAsync`.
+
+### Schemas
+
+<ApiList
+  items={[
+    'any',
+    'array',
+    'bigint',
+    'blob',
+    'boolean',
+    'custom',
+    'date',
+    'enum',
+    'file',
+    'function',
+    'instance',
+    'intersect',
+    'lazy',
+    'literal',
+    'looseObject',
+    'looseTuple',
+    'map',
+    'nan',
+    'never',
+    'nonNullable',
+    'nonNullish',
+    'nonOptional',
+    'null',
+    'nullable',
+    'nullish',
+    'number',
+    'object',
+    'objectWithRest',
+    'optional',
+    'picklist',
+    'promise',
+    'record',
+    'set',
+    'strictObject',
+    'strictTuple',
+    'string',
+    'symbol',
+    'tuple',
+    'tupleWithRest',
+    'undefined',
+    'undefinedable',
+    'union',
+    'unknown',
+    'variant',
+    'void',
+  ]}
+/>
+
+### Methods
+
+<ApiList items={['config', 'getDefault', 'getFallback']} />
+
+### Actions
+
+<ApiList
+  items={[
+    'base64',
+    'bic',
+    'brand',
+    'bytes',
+    'check',
+    'checkItems',
+    'creditCard',
+    'cuid2',
+    'decimal',
+    'description',
+    'email',
+    'emoji',
+    'empty',
+    'endsWith',
+    'everyItem',
+    'excludes',
+    'filterItems',
+    'findItem',
+    'finite',
+    'hash',
+    'hexadecimal',
+    'hexColor',
+    'imei',
+    'includes',
+    'integer',
+    'ip',
+    'ipv4',
+    'ipv6',
+    'isoDate',
+    'isoDateTime',
+    'isoTime',
+    'isoTimeSecond',
+    'isoTimestamp',
+    'isoWeek',
+    'length',
+    'mac',
+    'mac48',
+    'mac64',
+    'mapItems',
+    'maxBytes',
+    'maxLength',
+    'maxSize',
+    'maxValue',
+    'mimeType',
+    'minBytes',
+    'minLength',
+    'minSize',
+    'minValue',
+    'multipleOf',
+    'nonEmpty',
+    'notBytes',
+    'notLength',
+    'notSize',
+    'notValue',
+    'octal',
+    'partialCheck',
+    'rawCheck',
+    'rawTransform',
+    'readonly',
+    'reduceItems',
+    'regex',
+    'safeInteger',
+    'size',
+    'someItem',
+    'sortItem',
+    'startsWith',
+    'toLowerCase',
+    'toMaxValue',
+    'toMinValue',
+    'toUpperCase',
+    'transform',
+    'trim',
+    'trimEnd',
+    'trimStart',
+    'ulid',
+    'url',
+    'uuid',
+    'value',
+  ]}
+/>
+
+### Utils
+
+<ApiList items={['entriesFromList', 'isOfKind', 'isOfType']} />
+
+### Async
+
+<ApiList
+  items={[
+    'arrayAsync',
+    'checkAsync',
+    'customAsync',
+    'fallbackAsync',
+    'getDefaultsAsync',
+    'getFallbacksAsync',
+    'intersectAsync',
+    'lazyAsync',
+    'looseObjectAsync',
+    'looseTupleAsync',
+    'mapAsync',
+    'nonNullableAsync',
+    'nonNullishAsync',
+    'nonOptionalAsync',
+    'nullableAsync',
+    'nullishAsync',
+    'objectAsync',
+    'objectWithRestAsync',
+    'optionalAsync',
+    'parseAsync',
+    'parserAsync',
+    'partialCheckAsync',
+    'pipeAsync',
+    'rawCheckAsync',
+    'rawTransformAsync',
+    'recordAsync',
+    'safeParseAsync',
+    'safeParserAsync',
+    'setAsync',
+    'strictObjectAsync',
+    'strictTupleAsync',
+    'transformAsync',
+    'tupleAsync',
+    'tupleWithRestAsync',
+    'variantAsync',
+  ]}
+/>
diff --git a/website/src/routes/api/(async)/unionAsync/properties.ts b/website/src/routes/api/(async)/unionAsync/properties.ts
new file mode 100644
index 000000000..7deef5cbf
--- /dev/null
+++ b/website/src/routes/api/(async)/unionAsync/properties.ts
@@ -0,0 +1,76 @@
+import type { PropertyProps } from '~/components';
+
+export const properties: Record<string, PropertyProps> = {
+  TOptions: {
+    modifier: 'extends',
+    type: {
+      type: 'custom',
+      name: 'UnionOptionsAsync',
+      href: '../UnionOptionsAsync/',
+    },
+  },
+  TMessage: {
+    modifier: 'extends',
+    type: {
+      type: 'union',
+      options: [
+        {
+          type: 'custom',
+          name: 'ErrorMessage',
+          href: '../ErrorMessage/',
+          generics: [
+            {
+              type: 'custom',
+              name: 'UnionIssue',
+              href: '../UnionIssue/',
+              generics: [
+                {
+                  type: 'custom',
+                  name: 'InferIssue',
+                  href: '../InferIssue/',
+                  generics: [
+                    {
+                      type: 'custom',
+                      name: 'TOptions',
+                      indexes: ['number'],
+                    },
+                  ],
+                },
+              ],
+            },
+          ],
+        },
+        'undefined',
+      ],
+    },
+  },
+  options: {
+    type: {
+      type: 'custom',
+      name: 'TOptions',
+    },
+  },
+  message: {
+    type: {
+      type: 'custom',
+      name: 'TMessage',
+    },
+  },
+  Schema: {
+    type: {
+      type: 'custom',
+      name: 'UnionSchemaAsync',
+      href: '../UnionSchemaAsync/',
+      generics: [
+        {
+          type: 'custom',
+          name: 'TOptions',
+        },
+        {
+          type: 'custom',
+          name: 'TMessage',
+        },
+      ],
+    },
+  },
+};
diff --git a/website/src/routes/api/(methods)/config/index.mdx b/website/src/routes/api/(methods)/config/index.mdx
index ae0d156b4..76de8a95a 100644
--- a/website/src/routes/api/(methods)/config/index.mdx
+++ b/website/src/routes/api/(methods)/config/index.mdx
@@ -114,6 +114,7 @@ The following APIs can be combined with `config`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(methods)/fallback/index.mdx b/website/src/routes/api/(methods)/fallback/index.mdx
index 1c55f39f1..aaa4ee8e8 100644
--- a/website/src/routes/api/(methods)/fallback/index.mdx
+++ b/website/src/routes/api/(methods)/fallback/index.mdx
@@ -113,6 +113,7 @@ The following APIs can be combined with `fallback`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(methods)/getDefault/index.mdx b/website/src/routes/api/(methods)/getDefault/index.mdx
index 7f19715fb..6898fd5eb 100644
--- a/website/src/routes/api/(methods)/getDefault/index.mdx
+++ b/website/src/routes/api/(methods)/getDefault/index.mdx
@@ -92,6 +92,7 @@ The following APIs can be combined with `getDefault`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(methods)/getDefaults/index.mdx b/website/src/routes/api/(methods)/getDefaults/index.mdx
index a0b33a377..60fc3495c 100644
--- a/website/src/routes/api/(methods)/getDefaults/index.mdx
+++ b/website/src/routes/api/(methods)/getDefaults/index.mdx
@@ -106,6 +106,7 @@ The following APIs can be combined with `getDefaults`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(methods)/getFallback/index.mdx b/website/src/routes/api/(methods)/getFallback/index.mdx
index b2e869f86..8c7715662 100644
--- a/website/src/routes/api/(methods)/getFallback/index.mdx
+++ b/website/src/routes/api/(methods)/getFallback/index.mdx
@@ -92,6 +92,7 @@ The following APIs can be combined with `getFallback`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(methods)/getFallbacks/index.mdx b/website/src/routes/api/(methods)/getFallbacks/index.mdx
index 65a632370..b2c2af28b 100644
--- a/website/src/routes/api/(methods)/getFallbacks/index.mdx
+++ b/website/src/routes/api/(methods)/getFallbacks/index.mdx
@@ -106,6 +106,7 @@ The following APIs can be combined with `getFallbacks`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(methods)/is/index.mdx b/website/src/routes/api/(methods)/is/index.mdx
index 506aab3da..0de780b6e 100644
--- a/website/src/routes/api/(methods)/is/index.mdx
+++ b/website/src/routes/api/(methods)/is/index.mdx
@@ -93,6 +93,7 @@ The following APIs can be combined with `is`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(methods)/keyof/index.mdx b/website/src/routes/api/(methods)/keyof/index.mdx
index 019c18fb1..ca25d9ca5 100644
--- a/website/src/routes/api/(methods)/keyof/index.mdx
+++ b/website/src/routes/api/(methods)/keyof/index.mdx
@@ -72,6 +72,7 @@ The following APIs can be combined with `keyof`.
     'strictTuple',
     'tuple',
     'tupleWithRest',
+    'undefinedable',
     'union',
   ]}
 />
diff --git a/website/src/routes/api/(methods)/omit/index.mdx b/website/src/routes/api/(methods)/omit/index.mdx
index 262cbd840..a50ef4e1d 100644
--- a/website/src/routes/api/(methods)/omit/index.mdx
+++ b/website/src/routes/api/(methods)/omit/index.mdx
@@ -87,6 +87,7 @@ The following APIs can be combined with `omit`.
     'strictTuple',
     'tuple',
     'tupleWithRest',
+    'undefinedable',
     'union',
   ]}
 />
diff --git a/website/src/routes/api/(methods)/parse/index.mdx b/website/src/routes/api/(methods)/parse/index.mdx
index 5c54b915a..0223eaee4 100644
--- a/website/src/routes/api/(methods)/parse/index.mdx
+++ b/website/src/routes/api/(methods)/parse/index.mdx
@@ -99,6 +99,7 @@ The following APIs can be combined with `parse`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(methods)/parser/index.mdx b/website/src/routes/api/(methods)/parser/index.mdx
index 90a1c16b7..34ec74749 100644
--- a/website/src/routes/api/(methods)/parser/index.mdx
+++ b/website/src/routes/api/(methods)/parser/index.mdx
@@ -95,6 +95,7 @@ The following APIs can be combined with `parser`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(methods)/partial/index.mdx b/website/src/routes/api/(methods)/partial/index.mdx
index a601810c5..9dc785bc2 100644
--- a/website/src/routes/api/(methods)/partial/index.mdx
+++ b/website/src/routes/api/(methods)/partial/index.mdx
@@ -100,6 +100,7 @@ The following APIs can be combined with `partial`.
     'strictTuple',
     'tuple',
     'tupleWithRest',
+    'undefinedable',
     'union',
   ]}
 />
diff --git a/website/src/routes/api/(methods)/pick/index.mdx b/website/src/routes/api/(methods)/pick/index.mdx
index 535d5262e..acaaefed4 100644
--- a/website/src/routes/api/(methods)/pick/index.mdx
+++ b/website/src/routes/api/(methods)/pick/index.mdx
@@ -87,6 +87,7 @@ The following APIs can be combined with `pick`.
     'strictTuple',
     'tuple',
     'tupleWithRest',
+    'undefinedable',
     'union',
   ]}
 />
diff --git a/website/src/routes/api/(methods)/pipe/index.mdx b/website/src/routes/api/(methods)/pipe/index.mdx
index 6f4ba987d..5816816f8 100644
--- a/website/src/routes/api/(methods)/pipe/index.mdx
+++ b/website/src/routes/api/(methods)/pipe/index.mdx
@@ -114,6 +114,7 @@ The following APIs can be combined with `pipe`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(methods)/required/index.mdx b/website/src/routes/api/(methods)/required/index.mdx
index cfb263f3f..e825c78d7 100644
--- a/website/src/routes/api/(methods)/required/index.mdx
+++ b/website/src/routes/api/(methods)/required/index.mdx
@@ -102,6 +102,7 @@ The following APIs can be combined with `required`.
     'strictTuple',
     'tuple',
     'tupleWithRest',
+    'undefinedable',
     'union',
   ]}
 />
diff --git a/website/src/routes/api/(methods)/safeParse/index.mdx b/website/src/routes/api/(methods)/safeParse/index.mdx
index e5f8b24b4..e65403c93 100644
--- a/website/src/routes/api/(methods)/safeParse/index.mdx
+++ b/website/src/routes/api/(methods)/safeParse/index.mdx
@@ -94,6 +94,7 @@ The following APIs can be combined with `safeParse`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(methods)/safeParser/index.mdx b/website/src/routes/api/(methods)/safeParser/index.mdx
index 0fb3d55a5..0aa7ff9f7 100644
--- a/website/src/routes/api/(methods)/safeParser/index.mdx
+++ b/website/src/routes/api/(methods)/safeParser/index.mdx
@@ -95,6 +95,7 @@ The following APIs can be combined with `safeParser`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(methods)/unwrap/index.mdx b/website/src/routes/api/(methods)/unwrap/index.mdx
index eb310e5d9..81ce85495 100644
--- a/website/src/routes/api/(methods)/unwrap/index.mdx
+++ b/website/src/routes/api/(methods)/unwrap/index.mdx
@@ -56,6 +56,7 @@ The following APIs can be combined with `unwrap`.
     'nullable',
     'nullish',
     'optional',
+    'undefinedable',
   ]}
 />
 
diff --git a/website/src/routes/api/(schemas)/any/index.mdx b/website/src/routes/api/(schemas)/any/index.mdx
index 5b0675bd9..94a56fded 100644
--- a/website/src/routes/api/(schemas)/any/index.mdx
+++ b/website/src/routes/api/(schemas)/any/index.mdx
@@ -53,6 +53,7 @@ The following APIs can be combined with `any`.
     'strictTuple',
     'tuple',
     'tupleWithRest',
+    'undefinedable',
     'union',
   ]}
 />
diff --git a/website/src/routes/api/(schemas)/array/index.mdx b/website/src/routes/api/(schemas)/array/index.mdx
index 811fdab94..0286fe7f1 100644
--- a/website/src/routes/api/(schemas)/array/index.mdx
+++ b/website/src/routes/api/(schemas)/array/index.mdx
@@ -130,6 +130,7 @@ The following APIs can be combined with `array`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(schemas)/bigint/index.mdx b/website/src/routes/api/(schemas)/bigint/index.mdx
index 9357de56c..aa6d82fc7 100644
--- a/website/src/routes/api/(schemas)/bigint/index.mdx
+++ b/website/src/routes/api/(schemas)/bigint/index.mdx
@@ -81,6 +81,7 @@ The following APIs can be combined with `bigint`.
     'strictTuple',
     'tuple',
     'tupleWithRest',
+    'undefinedable',
     'union',
   ]}
 />
diff --git a/website/src/routes/api/(schemas)/blob/index.mdx b/website/src/routes/api/(schemas)/blob/index.mdx
index 7f6259ea5..2a8edb927 100644
--- a/website/src/routes/api/(schemas)/blob/index.mdx
+++ b/website/src/routes/api/(schemas)/blob/index.mdx
@@ -79,6 +79,7 @@ The following APIs can be combined with `blob`.
     'strictTuple',
     'tuple',
     'tupleWithRest',
+    'undefinedable',
     'union',
   ]}
 />
diff --git a/website/src/routes/api/(schemas)/boolean/index.mdx b/website/src/routes/api/(schemas)/boolean/index.mdx
index 5399d5ebf..794b369f1 100644
--- a/website/src/routes/api/(schemas)/boolean/index.mdx
+++ b/website/src/routes/api/(schemas)/boolean/index.mdx
@@ -77,6 +77,7 @@ The following APIs can be combined with `boolean`.
     'strictTuple',
     'tuple',
     'tupleWithRest',
+    'undefinedable',
     'union',
   ]}
 />
diff --git a/website/src/routes/api/(schemas)/custom/index.mdx b/website/src/routes/api/(schemas)/custom/index.mdx
index e0ace0339..8c866a639 100644
--- a/website/src/routes/api/(schemas)/custom/index.mdx
+++ b/website/src/routes/api/(schemas)/custom/index.mdx
@@ -82,6 +82,7 @@ The following APIs can be combined with `custom`.
     'strictTuple',
     'tuple',
     'tupleWithRest',
+    'undefinedable',
     'union',
   ]}
 />
diff --git a/website/src/routes/api/(schemas)/date/index.mdx b/website/src/routes/api/(schemas)/date/index.mdx
index 6159ff584..0ada973d7 100644
--- a/website/src/routes/api/(schemas)/date/index.mdx
+++ b/website/src/routes/api/(schemas)/date/index.mdx
@@ -86,6 +86,7 @@ The following APIs can be combined with `date`.
     'strictTuple',
     'tuple',
     'tupleWithRest',
+    'undefinedable',
     'union',
   ]}
 />
diff --git a/website/src/routes/api/(schemas)/enum/index.mdx b/website/src/routes/api/(schemas)/enum/index.mdx
index e1bf91c4e..524940333 100644
--- a/website/src/routes/api/(schemas)/enum/index.mdx
+++ b/website/src/routes/api/(schemas)/enum/index.mdx
@@ -80,6 +80,7 @@ The following APIs can be combined with `enum`.
     'strictTuple',
     'tuple',
     'tupleWithRest',
+    'undefinedable',
     'union',
   ]}
 />
diff --git a/website/src/routes/api/(schemas)/file/index.mdx b/website/src/routes/api/(schemas)/file/index.mdx
index 5b85a0784..7238da78c 100644
--- a/website/src/routes/api/(schemas)/file/index.mdx
+++ b/website/src/routes/api/(schemas)/file/index.mdx
@@ -79,6 +79,7 @@ The following APIs can be combined with `file`.
     'strictTuple',
     'tuple',
     'tupleWithRest',
+    'undefinedable',
     'union',
   ]}
 />
diff --git a/website/src/routes/api/(schemas)/function/index.mdx b/website/src/routes/api/(schemas)/function/index.mdx
index 8bfc168ea..4cc5de325 100644
--- a/website/src/routes/api/(schemas)/function/index.mdx
+++ b/website/src/routes/api/(schemas)/function/index.mdx
@@ -61,6 +61,7 @@ The following APIs can be combined with `function`.
     'strictTuple',
     'tuple',
     'tupleWithRest',
+    'undefinedable',
     'union',
   ]}
 />
diff --git a/website/src/routes/api/(schemas)/instance/index.mdx b/website/src/routes/api/(schemas)/instance/index.mdx
index ba21047c6..01f01b696 100644
--- a/website/src/routes/api/(schemas)/instance/index.mdx
+++ b/website/src/routes/api/(schemas)/instance/index.mdx
@@ -87,6 +87,7 @@ The following APIs can be combined with `instance`.
     'strictTuple',
     'tuple',
     'tupleWithRest',
+    'undefinedable',
     'union',
   ]}
 />
diff --git a/website/src/routes/api/(schemas)/intersect/index.mdx b/website/src/routes/api/(schemas)/intersect/index.mdx
index 0fde37503..93fa38f33 100644
--- a/website/src/routes/api/(schemas)/intersect/index.mdx
+++ b/website/src/routes/api/(schemas)/intersect/index.mdx
@@ -102,6 +102,7 @@ The following APIs can be combined with `intersect`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(schemas)/lazy/index.mdx b/website/src/routes/api/(schemas)/lazy/index.mdx
index 64cad44df..f9d7f09a2 100644
--- a/website/src/routes/api/(schemas)/lazy/index.mdx
+++ b/website/src/routes/api/(schemas)/lazy/index.mdx
@@ -139,6 +139,7 @@ The following APIs can be combined with `lazy`.
     'undefined',
     'union',
     'unionWithRest',
+    'undefinedable',
     'unknown',
     'variant',
     'void',
diff --git a/website/src/routes/api/(schemas)/literal/index.mdx b/website/src/routes/api/(schemas)/literal/index.mdx
index 4dee4c7a8..d50c40e48 100644
--- a/website/src/routes/api/(schemas)/literal/index.mdx
+++ b/website/src/routes/api/(schemas)/literal/index.mdx
@@ -91,6 +91,7 @@ The following APIs can be combined with `literal`.
     'strictTuple',
     'tuple',
     'tupleWithRest',
+    'undefinedable',
     'union',
   ]}
 />
diff --git a/website/src/routes/api/(schemas)/looseObject/index.mdx b/website/src/routes/api/(schemas)/looseObject/index.mdx
index 6ed3710c1..251a4826d 100644
--- a/website/src/routes/api/(schemas)/looseObject/index.mdx
+++ b/website/src/routes/api/(schemas)/looseObject/index.mdx
@@ -142,6 +142,7 @@ The following APIs can be combined with `looseObject`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(schemas)/looseTuple/index.mdx b/website/src/routes/api/(schemas)/looseTuple/index.mdx
index b9b58e598..ad51bbfef 100644
--- a/website/src/routes/api/(schemas)/looseTuple/index.mdx
+++ b/website/src/routes/api/(schemas)/looseTuple/index.mdx
@@ -97,6 +97,7 @@ The following APIs can be combined with `looseTuple`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(schemas)/map/index.mdx b/website/src/routes/api/(schemas)/map/index.mdx
index 6cfd58032..42cb25df2 100644
--- a/website/src/routes/api/(schemas)/map/index.mdx
+++ b/website/src/routes/api/(schemas)/map/index.mdx
@@ -104,6 +104,7 @@ The following APIs can be combined with `map`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(schemas)/nan/index.mdx b/website/src/routes/api/(schemas)/nan/index.mdx
index 740d4206d..14468d037 100644
--- a/website/src/routes/api/(schemas)/nan/index.mdx
+++ b/website/src/routes/api/(schemas)/nan/index.mdx
@@ -61,6 +61,7 @@ The following APIs can be combined with `nan`.
     'strictTuple',
     'tuple',
     'tupleWithRest',
+    'undefinedable',
     'union',
   ]}
 />
diff --git a/website/src/routes/api/(schemas)/never/index.mdx b/website/src/routes/api/(schemas)/never/index.mdx
index 2976649af..890eb4847 100644
--- a/website/src/routes/api/(schemas)/never/index.mdx
+++ b/website/src/routes/api/(schemas)/never/index.mdx
@@ -61,6 +61,7 @@ The following APIs can be combined with `never`.
     'strictTuple',
     'tuple',
     'tupleWithRest',
+    'undefinedable',
     'union',
   ]}
 />
diff --git a/website/src/routes/api/(schemas)/nonNullable/index.mdx b/website/src/routes/api/(schemas)/nonNullable/index.mdx
index f98674a12..2cc635b46 100644
--- a/website/src/routes/api/(schemas)/nonNullable/index.mdx
+++ b/website/src/routes/api/(schemas)/nonNullable/index.mdx
@@ -106,6 +106,7 @@ The following APIs can be combined with `nonNullable`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(schemas)/nonNullish/index.mdx b/website/src/routes/api/(schemas)/nonNullish/index.mdx
index 69b3ad962..3fed2fdd0 100644
--- a/website/src/routes/api/(schemas)/nonNullish/index.mdx
+++ b/website/src/routes/api/(schemas)/nonNullish/index.mdx
@@ -106,6 +106,7 @@ The following APIs can be combined with `nonNullish`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(schemas)/nonOptional/index.mdx b/website/src/routes/api/(schemas)/nonOptional/index.mdx
index abfd03d33..e737e7ca2 100644
--- a/website/src/routes/api/(schemas)/nonOptional/index.mdx
+++ b/website/src/routes/api/(schemas)/nonOptional/index.mdx
@@ -106,6 +106,7 @@ The following APIs can be combined with `nonOptional`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(schemas)/null/index.mdx b/website/src/routes/api/(schemas)/null/index.mdx
index bc3d24c80..d854ecf5c 100644
--- a/website/src/routes/api/(schemas)/null/index.mdx
+++ b/website/src/routes/api/(schemas)/null/index.mdx
@@ -61,6 +61,7 @@ The following APIs can be combined with `null`.
     'strictTuple',
     'tuple',
     'tupleWithRest',
+    'undefinedable',
     'union',
   ]}
 />
diff --git a/website/src/routes/api/(schemas)/nullable/index.mdx b/website/src/routes/api/(schemas)/nullable/index.mdx
index ef02cfbda..8de6bf1ee 100644
--- a/website/src/routes/api/(schemas)/nullable/index.mdx
+++ b/website/src/routes/api/(schemas)/nullable/index.mdx
@@ -127,6 +127,7 @@ The following APIs can be combined with `nullable`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(schemas)/nullish/index.mdx b/website/src/routes/api/(schemas)/nullish/index.mdx
index 134ca9106..f632517a2 100644
--- a/website/src/routes/api/(schemas)/nullish/index.mdx
+++ b/website/src/routes/api/(schemas)/nullish/index.mdx
@@ -127,6 +127,7 @@ The following APIs can be combined with `nullish`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(schemas)/number/index.mdx b/website/src/routes/api/(schemas)/number/index.mdx
index 0d96833ff..7a0213562 100644
--- a/website/src/routes/api/(schemas)/number/index.mdx
+++ b/website/src/routes/api/(schemas)/number/index.mdx
@@ -89,6 +89,7 @@ The following APIs can be combined with `number`.
     'strictTuple',
     'tuple',
     'tupleWithRest',
+    'undefinedable',
     'union',
   ]}
 />
diff --git a/website/src/routes/api/(schemas)/object/index.mdx b/website/src/routes/api/(schemas)/object/index.mdx
index 6f95a3b81..5646c74c9 100644
--- a/website/src/routes/api/(schemas)/object/index.mdx
+++ b/website/src/routes/api/(schemas)/object/index.mdx
@@ -142,6 +142,7 @@ The following APIs can be combined with `object`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(schemas)/objectWithRest/index.mdx b/website/src/routes/api/(schemas)/objectWithRest/index.mdx
index 22c4f5d95..0e2ea6aec 100644
--- a/website/src/routes/api/(schemas)/objectWithRest/index.mdx
+++ b/website/src/routes/api/(schemas)/objectWithRest/index.mdx
@@ -160,6 +160,7 @@ The following APIs can be combined with `objectWithRest`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(schemas)/optional/index.mdx b/website/src/routes/api/(schemas)/optional/index.mdx
index 926dd814d..af32a7ec9 100644
--- a/website/src/routes/api/(schemas)/optional/index.mdx
+++ b/website/src/routes/api/(schemas)/optional/index.mdx
@@ -127,6 +127,7 @@ The following APIs can be combined with `optional`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(schemas)/picklist/index.mdx b/website/src/routes/api/(schemas)/picklist/index.mdx
index d160a4a58..ae54fb89a 100644
--- a/website/src/routes/api/(schemas)/picklist/index.mdx
+++ b/website/src/routes/api/(schemas)/picklist/index.mdx
@@ -96,6 +96,7 @@ The following APIs can be combined with `picklist`.
     'strictTuple',
     'tuple',
     'tupleWithRest',
+    'undefinedable',
     'union',
   ]}
 />
diff --git a/website/src/routes/api/(schemas)/promise/index.mdx b/website/src/routes/api/(schemas)/promise/index.mdx
index ba4d9a338..323604369 100644
--- a/website/src/routes/api/(schemas)/promise/index.mdx
+++ b/website/src/routes/api/(schemas)/promise/index.mdx
@@ -77,6 +77,7 @@ The following APIs can be combined with `promise`.
     'strictTuple',
     'tuple',
     'tupleWithRest',
+    'undefinedable',
     'union',
   ]}
 />
diff --git a/website/src/routes/api/(schemas)/record/index.mdx b/website/src/routes/api/(schemas)/record/index.mdx
index 5d75055be..e083cccbc 100644
--- a/website/src/routes/api/(schemas)/record/index.mdx
+++ b/website/src/routes/api/(schemas)/record/index.mdx
@@ -138,6 +138,7 @@ The following APIs can be combined with `record`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(schemas)/set/index.mdx b/website/src/routes/api/(schemas)/set/index.mdx
index 527751a55..181f0af02 100644
--- a/website/src/routes/api/(schemas)/set/index.mdx
+++ b/website/src/routes/api/(schemas)/set/index.mdx
@@ -102,6 +102,7 @@ The following APIs can be combined with `set`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(schemas)/strictObject/index.mdx b/website/src/routes/api/(schemas)/strictObject/index.mdx
index 2ee6fb76f..2aea51755 100644
--- a/website/src/routes/api/(schemas)/strictObject/index.mdx
+++ b/website/src/routes/api/(schemas)/strictObject/index.mdx
@@ -142,6 +142,7 @@ The following APIs can be combined with `strictObject`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(schemas)/strictTuple/index.mdx b/website/src/routes/api/(schemas)/strictTuple/index.mdx
index 9d119ae87..3cd612891 100644
--- a/website/src/routes/api/(schemas)/strictTuple/index.mdx
+++ b/website/src/routes/api/(schemas)/strictTuple/index.mdx
@@ -97,6 +97,7 @@ The following APIs can be combined with `strictTuple`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(schemas)/string/index.mdx b/website/src/routes/api/(schemas)/string/index.mdx
index eb2f410f8..51be9e044 100644
--- a/website/src/routes/api/(schemas)/string/index.mdx
+++ b/website/src/routes/api/(schemas)/string/index.mdx
@@ -106,6 +106,7 @@ The following APIs can be combined with `string`.
     'strictTuple',
     'tuple',
     'tupleWithRest',
+    'undefinedable',
     'union',
   ]}
 />
diff --git a/website/src/routes/api/(schemas)/symbol/index.mdx b/website/src/routes/api/(schemas)/symbol/index.mdx
index eaf7d3f07..22922812e 100644
--- a/website/src/routes/api/(schemas)/symbol/index.mdx
+++ b/website/src/routes/api/(schemas)/symbol/index.mdx
@@ -74,6 +74,7 @@ The following APIs can be combined with `symbol`.
     'strictTuple',
     'tuple',
     'tupleWithRest',
+    'undefinedable',
     'union',
   ]}
 />
diff --git a/website/src/routes/api/(schemas)/tuple/index.mdx b/website/src/routes/api/(schemas)/tuple/index.mdx
index 0388c1b01..9a19a73bd 100644
--- a/website/src/routes/api/(schemas)/tuple/index.mdx
+++ b/website/src/routes/api/(schemas)/tuple/index.mdx
@@ -97,6 +97,7 @@ The following APIs can be combined with `tuple`.
     'symbol',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(schemas)/tupleWithRest/index.mdx b/website/src/routes/api/(schemas)/tupleWithRest/index.mdx
index bfc242852..bb42510c8 100644
--- a/website/src/routes/api/(schemas)/tupleWithRest/index.mdx
+++ b/website/src/routes/api/(schemas)/tupleWithRest/index.mdx
@@ -100,6 +100,7 @@ The following APIs can be combined with `tupleWithRest`.
     'symbol',
     'tuple',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(schemas)/undefined/index.mdx b/website/src/routes/api/(schemas)/undefined/index.mdx
index 9b09babac..1d1491829 100644
--- a/website/src/routes/api/(schemas)/undefined/index.mdx
+++ b/website/src/routes/api/(schemas)/undefined/index.mdx
@@ -61,6 +61,7 @@ The following APIs can be combined with `undefined`.
     'strictTuple',
     'tuple',
     'tupleWithRest',
+    'undefinedable',
     'union',
   ]}
 />
diff --git a/website/src/routes/api/(schemas)/undefinedable/index.mdx b/website/src/routes/api/(schemas)/undefinedable/index.mdx
new file mode 100644
index 000000000..6e74212f0
--- /dev/null
+++ b/website/src/routes/api/(schemas)/undefinedable/index.mdx
@@ -0,0 +1,179 @@
+---
+title: undefinedable
+description: Creates an undefinedable schema.
+source: /schemas/undefinedable/undefinedable.ts
+contributors:
+  - fabian-hiller
+---
+
+import { Link } from '@builder.io/qwik-city';
+import { ApiList, Property } from '~/components';
+import { properties } from './properties';
+
+# undefinedable
+
+Creates an undefinedable schema.
+
+```ts
+const Schema = v.undefinedable<TWrapped, TDefault>(wrapped, default_);
+```
+
+## Generics
+
+- `TWrapped` <Property {...properties.TWrapped} />
+- `TDefault` <Property {...properties.TDefault} />
+
+## Parameters
+
+- `wrapped` <Property {...properties.wrapped} />
+- `default_` {/* prettier-ignore */}<Property {...properties.default_} />
+
+### Explanation
+
+With `undefinedable` the validation of your schema will pass `undefined` inputs, and if you specify a `default_` input value, the schema will use it if the input is `undefined`. For this reason, the output type may differ from the input type of the schema.
+
+> `undefinedable` behaves exactly the same as <Link href="../optional/">`optional`</Link> at runtime. The only difference is the input and output type when used for object entries. While <Link href="../optional/">`optional`</Link> adds a question mark to the key, `undefinedable` does not.
+
+> Note that `undefinedable` does not accept `null` as an input. If you want to accept `null` inputs, use <Link href="../nullable/">`nullable`</Link>, and if you want to accept `null` and `undefined` inputs, use <Link href="../nullish/">`nullish`</Link> instead. Also, if you want to set a default output value for any invalid input, you should use <Link href="../fallback/">`fallback`</Link> instead.
+
+## Returns
+
+- `Schema` <Property {...properties.Schema} />
+
+## Examples
+
+The following examples show how `undefinedable` can be used.
+
+### Undefinedable string schema
+
+Schema that accepts `string` and `undefined`.
+
+```ts
+const UndefinedableStringSchema = v.undefinedable(
+  v.string(),
+  "I'm the default!"
+);
+```
+
+### Undefinedable date schema
+
+Schema that accepts [`Date`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date) and `undefined`.
+
+> By using a function as the `default_` parameter, the schema will return a new [`Date`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date) instance each time the input is `undefined`.
+
+```ts
+const UndefinedableDateSchema = v.undefinedable(v.date(), () => new Date());
+```
+
+### Undefinedable entry schema
+
+Object schema with an undefinedable entry.
+
+```ts
+const UndefinedableEntrySchema = v.object({
+  key: v.undefinedable(v.string()),
+});
+```
+
+### Unwrap undefinedable schema
+
+Use <Link href="../unwrap/">`unwrap`</Link> to undo the effect of `undefinedable`.
+
+```ts
+const UndefinedableNumberSchema = v.undefinedable(v.number());
+const NumberSchema = v.unwrap(UndefinedableNumberSchema);
+```
+
+## Related
+
+The following APIs can be combined with `undefinedable`.
+
+### Schemas
+
+<ApiList
+  items={[
+    'any',
+    'array',
+    'bigint',
+    'blob',
+    'boolean',
+    'custom',
+    'date',
+    'enum',
+    'file',
+    'function',
+    'instance',
+    'intersect',
+    'lazy',
+    'literal',
+    'looseObject',
+    'looseTuple',
+    'map',
+    'nan',
+    'never',
+    'nonNullable',
+    'nonNullish',
+    'nonUndefinedable',
+    'null',
+    'nullable',
+    'nullish',
+    'number',
+    'object',
+    'objectWithRest',
+    'picklist',
+    'promise',
+    'record',
+    'set',
+    'strictObject',
+    'strictTuple',
+    'string',
+    'symbol',
+    'tuple',
+    'tupleWithRest',
+    'undefined',
+    'undefinedable',
+    'union',
+    'unknown',
+    'variant',
+    'void',
+  ]}
+/>
+
+### Methods
+
+<ApiList
+  items={[
+    'config',
+    'fallback',
+    'getDefault',
+    'getDefaults',
+    'getFallback',
+    'getFallbacks',
+    'is',
+    'parse',
+    'parser',
+    'pipe',
+    'safeParse',
+    'safeParser',
+    'unwrap',
+  ]}
+/>
+
+### Actions
+
+<ApiList
+  items={[
+    'check',
+    'brand',
+    'description',
+    'partialCheck',
+    'rawCheck',
+    'rawTransform',
+    'readonly',
+    'transform',
+  ]}
+/>
+
+### Utils
+
+<ApiList items={['entriesFromList', 'isOfKind', 'isOfType']} />
diff --git a/website/src/routes/api/(schemas)/undefinedable/properties.ts b/website/src/routes/api/(schemas)/undefinedable/properties.ts
new file mode 100644
index 000000000..18d48a10b
--- /dev/null
+++ b/website/src/routes/api/(schemas)/undefinedable/properties.ts
@@ -0,0 +1,71 @@
+import type { PropertyProps } from '~/components';
+
+export const properties: Record<string, PropertyProps> = {
+  TWrapped: {
+    modifier: 'extends',
+    type: {
+      type: 'custom',
+      name: 'BaseSchema',
+      href: '../BaseSchema/',
+      generics: [
+        'unknown',
+        'unknown',
+        {
+          type: 'custom',
+          name: 'BaseIssue',
+          href: '../BaseIssue/',
+          generics: ['unknown'],
+        },
+      ],
+    },
+  },
+  TDefault: {
+    modifier: 'extends',
+    type: {
+      type: 'union',
+      options: [
+        {
+          type: 'custom',
+          name: 'Default',
+          href: '../Default/',
+          generics: [
+            {
+              type: 'custom',
+              name: 'TWrapped',
+            },
+          ],
+        },
+        'never',
+      ],
+    },
+  },
+  wrapped: {
+    type: {
+      type: 'custom',
+      name: 'TWrapped',
+    },
+  },
+  default_: {
+    type: {
+      type: 'custom',
+      name: 'TDefault',
+    },
+  },
+  Schema: {
+    type: {
+      type: 'custom',
+      name: 'UndefinedableSchema',
+      href: '../UndefinedableSchema/',
+      generics: [
+        {
+          type: 'custom',
+          name: 'TWrapped',
+        },
+        {
+          type: 'custom',
+          name: 'TDefault',
+        },
+      ],
+    },
+  },
+};
diff --git a/website/src/routes/api/(schemas)/union/index.mdx b/website/src/routes/api/(schemas)/union/index.mdx
index 51d8941c0..9964e00e1 100644
--- a/website/src/routes/api/(schemas)/union/index.mdx
+++ b/website/src/routes/api/(schemas)/union/index.mdx
@@ -118,6 +118,7 @@ The following APIs can be combined with `union`.
     'tuple',
     'tupleWithRest',
     'undefined',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
diff --git a/website/src/routes/api/(schemas)/unknown/index.mdx b/website/src/routes/api/(schemas)/unknown/index.mdx
index c4bc7e4ea..689994b72 100644
--- a/website/src/routes/api/(schemas)/unknown/index.mdx
+++ b/website/src/routes/api/(schemas)/unknown/index.mdx
@@ -53,6 +53,7 @@ The following APIs can be combined with `unknwon`.
     'strictTuple',
     'tuple',
     'tupleWithRest',
+    'undefinedable',
     'union',
   ]}
 />
diff --git a/website/src/routes/api/(schemas)/void/index.mdx b/website/src/routes/api/(schemas)/void/index.mdx
index 89e3efdc8..7e309e385 100644
--- a/website/src/routes/api/(schemas)/void/index.mdx
+++ b/website/src/routes/api/(schemas)/void/index.mdx
@@ -61,6 +61,7 @@ The following APIs can be combined with `void`.
     'strictTuple',
     'tuple',
     'tupleWithRest',
+    'undefinedable',
     'union',
   ]}
 />
diff --git a/website/src/routes/api/(types)/UndefinedableSchema/index.mdx b/website/src/routes/api/(types)/UndefinedableSchema/index.mdx
new file mode 100644
index 000000000..cc88ef48b
--- /dev/null
+++ b/website/src/routes/api/(types)/UndefinedableSchema/index.mdx
@@ -0,0 +1,28 @@
+---
+title: UndefinedableSchema
+description: Undefinedable schema type.
+contributors:
+  - fabian-hiller
+  - sqmasep
+---
+
+import { Property } from '~/components';
+import { properties } from './properties';
+
+# UndefinedableSchema
+
+Undefinedable schema type.
+
+## Generics
+
+- `TWrapped` <Property {...properties.TWrapped} />
+- `TDefault` <Property {...properties.TDefault} />
+
+## Definition
+
+- `UndefinedableSchema` <Property {...properties.BaseSchema} />
+  - `type` <Property {...properties.type} />
+  - `reference` <Property {...properties.reference} />
+  - `expects` <Property {...properties.expects} />
+  - `wrapped` <Property {...properties.wrapped} />
+  - `default` <Property {...properties.default} />
diff --git a/website/src/routes/api/(types)/UndefinedableSchema/properties.ts b/website/src/routes/api/(types)/UndefinedableSchema/properties.ts
new file mode 100644
index 000000000..e41e994aa
--- /dev/null
+++ b/website/src/routes/api/(types)/UndefinedableSchema/properties.ts
@@ -0,0 +1,141 @@
+import type { PropertyProps } from '~/components';
+
+export const properties: Record<string, PropertyProps> = {
+  TWrapped: {
+    modifier: 'extends',
+    type: {
+      type: 'custom',
+      name: 'BaseSchema',
+      href: '../BaseSchema/',
+      generics: [
+        'unknown',
+        'unknown',
+        {
+          type: 'custom',
+          name: 'BaseIssue',
+          href: '../BaseIssue/',
+          generics: ['unknown'],
+        },
+      ],
+    },
+  },
+  TDefault: {
+    modifier: 'extends',
+    type: {
+      type: 'custom',
+      name: 'Default',
+      href: '../Default/',
+      generics: [
+        {
+          type: 'custom',
+          name: 'TWrapped',
+        },
+        'undefined',
+      ],
+    },
+  },
+  BaseSchema: {
+    modifier: 'extends',
+    type: {
+      type: 'custom',
+      name: 'BaseSchema',
+      href: '../BaseSchema/',
+      generics: [
+        {
+          type: 'union',
+          options: [
+            {
+              type: 'custom',
+              name: 'InferInput',
+              href: '../InferInput/',
+              generics: [
+                {
+                  type: 'custom',
+                  name: 'TWrapped',
+                },
+              ],
+            },
+            'undefined',
+          ],
+        },
+        {
+          type: 'custom',
+          name: 'InferUndefinedableOutput',
+          href: '../InferUndefinedableOutput/',
+          generics: [
+            {
+              type: 'custom',
+              name: 'TWrapped',
+            },
+            {
+              type: 'custom',
+              name: 'TDefault',
+            },
+          ],
+        },
+        {
+          type: 'custom',
+          name: 'InferIssue',
+          href: '../InferIssue/',
+          generics: [
+            {
+              type: 'custom',
+              name: 'TWrapped',
+            },
+          ],
+        },
+      ],
+    },
+  },
+  type: {
+    type: {
+      type: 'string',
+      value: 'undefinedable',
+    },
+  },
+  reference: {
+    type: {
+      type: 'custom',
+      modifier: 'typeof',
+      name: 'undefinedable',
+      href: '../undefinedable/',
+    },
+  },
+  expects: {
+    type: {
+      type: 'template',
+      parts: [
+        {
+          type: 'string',
+          value: '(',
+        },
+        {
+          type: 'custom',
+          name: 'TWrapped',
+          indexes: [
+            {
+              type: 'string',
+              value: 'expects',
+            },
+          ],
+        },
+        {
+          type: 'string',
+          value: ' | undefined)',
+        },
+      ],
+    },
+  },
+  wrapped: {
+    type: {
+      type: 'custom',
+      name: 'TWrapped',
+    },
+  },
+  default: {
+    type: {
+      type: 'custom',
+      name: 'TDefault',
+    },
+  },
+};
diff --git a/website/src/routes/api/(types)/UndefinedableSchemaAsync/index.mdx b/website/src/routes/api/(types)/UndefinedableSchemaAsync/index.mdx
new file mode 100644
index 000000000..3de24c86c
--- /dev/null
+++ b/website/src/routes/api/(types)/UndefinedableSchemaAsync/index.mdx
@@ -0,0 +1,27 @@
+---
+title: UndefinedableSchemaAsync
+description: Undefinedable schema async type.
+contributors:
+  - fabian-hiller
+---
+
+import { Property } from '~/components';
+import { properties } from './properties';
+
+# UndefinedableSchemaAsync
+
+Undefinedable schema async type.
+
+## Generics
+
+- `TWrapped` <Property {...properties.TWrapped} />
+- `TDefault` <Property {...properties.TDefault} />
+
+## Definition
+
+- `UndefinedableSchemaAsync` <Property {...properties.BaseSchemaAsync} />
+  - `type` <Property {...properties.type} />
+  - `reference` <Property {...properties.reference} />
+  - `expects` <Property {...properties.expects} />
+  - `wrapped` <Property {...properties.wrapped} />
+  - `default` <Property {...properties.default} />
diff --git a/website/src/routes/api/(types)/UndefinedableSchemaAsync/properties.ts b/website/src/routes/api/(types)/UndefinedableSchemaAsync/properties.ts
new file mode 100644
index 000000000..aab595c9e
--- /dev/null
+++ b/website/src/routes/api/(types)/UndefinedableSchemaAsync/properties.ts
@@ -0,0 +1,160 @@
+import type { PropertyProps } from '~/components';
+
+export const properties: Record<string, PropertyProps> = {
+  TWrapped: {
+    modifier: 'extends',
+    type: {
+      type: 'union',
+      options: [
+        {
+          type: 'custom',
+          name: 'BaseSchema',
+          href: '../BaseSchema/',
+          generics: [
+            'unknown',
+            'unknown',
+            {
+              type: 'custom',
+              name: 'BaseIssue',
+              href: '../BaseIssue/',
+              generics: ['unknown'],
+            },
+          ],
+        },
+        {
+          type: 'custom',
+          name: 'BaseSchemaAsync',
+          href: '../BaseSchemaAsync/',
+          generics: [
+            'unknown',
+            'unknown',
+            {
+              type: 'custom',
+              name: 'BaseIssue',
+              href: '../BaseIssue/',
+              generics: ['unknown'],
+            },
+          ],
+        },
+      ],
+    },
+  },
+  TDefault: {
+    modifier: 'extends',
+    type: {
+      type: 'custom',
+      name: 'DefaultAsync',
+      href: '../DefaultAsync/',
+      generics: [
+        {
+          type: 'custom',
+          name: 'TWrapped',
+        },
+        'undefined',
+      ],
+    },
+  },
+  BaseSchemaAsync: {
+    type: {
+      type: 'custom',
+      name: 'BaseSchemaAsync',
+      href: '../BaseSchemaAsync/',
+      generics: [
+        {
+          type: 'union',
+          options: [
+            {
+              type: 'custom',
+              name: 'InferInput',
+              href: '../InferInput/',
+              generics: [
+                {
+                  type: 'custom',
+                  name: 'TWrapped',
+                },
+              ],
+            },
+            'undefined',
+          ],
+        },
+        {
+          type: 'custom',
+          name: 'InferUndefinedableOutput',
+          href: '../InferUndefinedableOutput/',
+          generics: [
+            {
+              type: 'custom',
+              name: 'TWrapped',
+            },
+            {
+              type: 'custom',
+              name: 'TDefault',
+            },
+          ],
+        },
+        {
+          type: 'custom',
+          name: 'InferIssue',
+          href: '../InferIssue/',
+          generics: [
+            {
+              type: 'custom',
+              name: 'TWrapped',
+            },
+          ],
+        },
+      ],
+    },
+  },
+  type: {
+    type: {
+      type: 'string',
+      value: 'undefinedable',
+    },
+  },
+  reference: {
+    type: {
+      type: 'custom',
+      modifier: 'typeof',
+      name: 'undefinedableAsync',
+      href: '../undefinedableAsync/',
+    },
+  },
+  expects: {
+    type: {
+      type: 'template',
+      parts: [
+        {
+          type: 'string',
+          value: '(',
+        },
+        {
+          type: 'custom',
+          name: 'TWrapped',
+          indexes: [
+            {
+              type: 'string',
+              value: 'expects',
+            },
+          ],
+        },
+        {
+          type: 'string',
+          value: ' | undefined)',
+        },
+      ],
+    },
+  },
+  wrapped: {
+    type: {
+      type: 'custom',
+      name: 'TWrapped',
+    },
+  },
+  default: {
+    type: {
+      type: 'custom',
+      name: 'TDefault',
+    },
+  },
+};
diff --git a/website/src/routes/api/(utils)/entriesFromList/index.mdx b/website/src/routes/api/(utils)/entriesFromList/index.mdx
index c9b318034..8af47e0f8 100644
--- a/website/src/routes/api/(utils)/entriesFromList/index.mdx
+++ b/website/src/routes/api/(utils)/entriesFromList/index.mdx
@@ -87,6 +87,7 @@ The following APIs can be combined with `entriesFromList`.
     'symbol',
     'tuple',
     'undefined',
+    'undefinedable',
     'union',
     'unionWithRest',
     'unknown',
diff --git a/website/src/routes/api/menu.md b/website/src/routes/api/menu.md
index 4f0b792ad..de2bde510 100644
--- a/website/src/routes/api/menu.md
+++ b/website/src/routes/api/menu.md
@@ -42,6 +42,7 @@
 - [tuple](/api/tuple/)
 - [tupleWithRest](/api/tupleWithRest/)
 - [undefined](/api/undefined/)
+- [undefinedable](/api/undefinedable/)
 - [union](/api/union/)
 - [unknown](/api/unknown/)
 - [variant](/api/variant/)
@@ -217,6 +218,7 @@
 - [transformAsync](/api/transformAsync/)
 - [tupleAsync](/api/tupleAsync/)
 - [tupleWithRestAsync](/api/tupleWithRestAsync/)
+- [undefinedableAsync](/api/undefinedableAsync/)
 - [unionAsync](/api/unionAsync/)
 - [variantAsync](/api/variantAsync/)
 
@@ -561,6 +563,8 @@
 - [TypedDataset](/api/TypedDataset/)
 - [UlidAction](/api/UlidAction/)
 - [UlidIssue](/api/UlidIssue/)
+- [UndefinedableSchema](/api/UndefinedableSchema/)
+- [UndefinedableSchemaAsync](/api/UndefinedableSchemaAsync/)
 - [UndefinedIssue](/api/UndefinedIssue/)
 - [UndefinedSchema](/api/UndefinedSchema/)
 - [UnionOptions](/api/UnionOptions/)
diff --git a/website/src/routes/guides/(main-concepts)/infer-types/index.mdx b/website/src/routes/guides/(main-concepts)/infer-types/index.mdx
index 1a078146e..b1d56a3c1 100644
--- a/website/src/routes/guides/(main-concepts)/infer-types/index.mdx
+++ b/website/src/routes/guides/(main-concepts)/infer-types/index.mdx
@@ -33,7 +33,7 @@ type LoginInput = v.InferInput<typeof LoginSchema>; // { email: string; password
 
 ## Infer output types
 
-The output type differs from the input type only if you use <Link href="/api/optional/">`optional`</Link>, <Link href="/api/nullable/">`nullable`</Link> or <Link href="/api/nullish/">`nullish`</Link> with a default value or <Link href="/api/brand/">`brand`</Link>, <Link href="/api/readonly/">`readonly`</Link> or <Link href="/api/transform/">`transform`</Link> to transform the input or data type of a schema after validation. The output type corresponds to the output of <Link href="/api/parse/">`parse`</Link> and <Link href="/api/safeParse/">`safeParse`</Link>. To infer it, you use the utility type <Link href="/api/InferOutput/">`InferOutput`</Link>.
+The output type differs from the input type only if you use <Link href="/api/optional/">`optional`</Link>, <Link href="/api/nullable/">`nullable`</Link>, <Link href="/api/nullish/">`nullish`</Link> or <Link href="/api/undefinedable/">`undefinedable`</Link> with a default value or <Link href="/api/brand/">`brand`</Link>, <Link href="/api/readonly/">`readonly`</Link> or <Link href="/api/transform/">`transform`</Link> to transform the input or data type of a schema after validation. The output type corresponds to the output of <Link href="/api/parse/">`parse`</Link> and <Link href="/api/safeParse/">`safeParse`</Link>. To infer it, you use the utility type <Link href="/api/InferOutput/">`InferOutput`</Link>.
 
 ```ts
 import * as v from 'valibot';
diff --git a/website/src/routes/guides/(main-concepts)/schemas/index.mdx b/website/src/routes/guides/(main-concepts)/schemas/index.mdx
index 976130d48..ad5bfe295 100644
--- a/website/src/routes/guides/(main-concepts)/schemas/index.mdx
+++ b/website/src/routes/guides/(main-concepts)/schemas/index.mdx
@@ -121,6 +121,7 @@ Beyond primitive and complex values, I also provide schema functions for more sp
     'nullish',
     'optional',
     'picklist',
+    'undefinedable',
     'union',
     'unknown',
     'variant',
@@ -147,6 +148,7 @@ const NullableSchema = v.nullable(v.string()); // string | null
 const NullishSchema = v.nullish(v.string()); // string | null | undefined
 const OptionalSchema = v.optional(v.string()); // string | undefined
 const PicklistSchema = v.picklist(['a', 'b']); // 'a' | 'b'
+const UndefinedableSchema = v.undefinedable(v.string()); // string | undefined
 const UnionSchema = v.union([v.string(), v.number()]); // string | number
 const UnknownSchema = v.unknown(); // unknown
 const VariantSchema = v.variant('type', [
diff --git a/website/src/routes/guides/(schemas)/optionals/index.mdx b/website/src/routes/guides/(schemas)/optionals/index.mdx
index 159714463..520e0407e 100644
--- a/website/src/routes/guides/(schemas)/optionals/index.mdx
+++ b/website/src/routes/guides/(schemas)/optionals/index.mdx
@@ -11,11 +11,11 @@ import { Link } from '@builder.io/qwik-city';
 
 # Optionals
 
-It often happens that `undefined` or `null` should also be accepted instead of the value. To make the API more readable for this and to reduce boilerplate, I offer a shortcut for this functionality with <Link href="/api/optional/">`optional`</Link>, <Link href="/api/nullable/">`nullable`</Link> and <Link href="/api/nullish/">`nullish`</Link>.
+It often happens that `undefined` or `null` should also be accepted instead of the value. To make the API more readable for this and to reduce boilerplate, I offer a shortcut for this functionality with <Link href="/api/optional/">`optional`</Link>, <Link href="/api/nullable/">`nullable`</Link>, <Link href="/api/nullish/">`nullish`</Link> and <Link href="/api/undefinedable/">`undefinedable`</Link>.
 
 ## How it works
 
-To accept `undefined` or `null` besides your actual value, you just have to wrap the schema in <Link href="/api/optional/">`optional`</Link>, <Link href="/api/nullable/">`nullable`</Link> and <Link href="/api/nullish/">`nullish`</Link>.
+To accept `undefined` or `null` besides your actual value, you just have to wrap the schema in <Link href="/api/optional/">`optional`</Link>, <Link href="/api/nullable/">`nullable`</Link>, and <Link href="/api/undefinedable/">`undefinedable`</Link>.
 
 ```ts
 import * as v from 'valibot';
@@ -23,6 +23,7 @@ import * as v from 'valibot';
 const OptionalStringSchema = v.optional(v.string()); // string | undefined
 const NullableStringSchema = v.nullable(v.string()); // string | null
 const NullishStringSchema = v.nullish(v.string()); // string | null | undefined
+const UndefinedableStringSchema = v.undefinedable(v.string()); // string | undefined
 ```
 
 ### Use in objects
@@ -37,7 +38,7 @@ const OptionalKeySchema = v.object({ key: v.optional(v.string()) }); // { key?:
 
 ## Default values
 
-The special thing about <Link href="/api/optional/">`optional`</Link>, <Link href="/api/nullable/">`nullable`</Link> and <Link href="/api/nullish/">`nullish`</Link> is that the schema functions accept a default value as the second argument. Depending on the schema function, this default value is always used if the input is `undefined` or `null`.
+The special thing about <Link href="/api/optional/">`optional`</Link>, <Link href="/api/nullable/">`nullable`</Link>, <Link href="/api/nullish/">`nullish`</Link> and <Link href="/api/undefinedable/">`undefinedable`</Link> is that the schema functions accept a default value as the second argument. Depending on the schema function, this default value is always used if the input is `undefined` or `null`.
 
 ```ts
 import * as v from 'valibot';