diff --git a/.changeset/cuddly-dodos-arrive.md b/.changeset/cuddly-dodos-arrive.md
new file mode 100644
index 0000000000..df027f613f
--- /dev/null
+++ b/.changeset/cuddly-dodos-arrive.md
@@ -0,0 +1,6 @@
+---
+"@effect/platform-node": patch
+"@effect/platform": patch
+---
+
+use ReadonlyRecord for storing cookies
diff --git a/.changeset/eight-seals-tie.md b/.changeset/eight-seals-tie.md
new file mode 100644
index 0000000000..b283d3281a
--- /dev/null
+++ b/.changeset/eight-seals-tie.md
@@ -0,0 +1,7 @@
+---
+"@effect/platform-node": patch
+"@effect/platform-bun": patch
+"@effect/platform": patch
+---
+
+add set-cookie headers in Http.response.toWeb
diff --git a/packages/platform-bun/src/internal/http/server.ts b/packages/platform-bun/src/internal/http/server.ts
index 7f31b9bf4c..22bf22ddec 100644
--- a/packages/platform-bun/src/internal/http/server.ts
+++ b/packages/platform-bun/src/internal/http/server.ts
@@ -126,8 +126,7 @@ const makeResponse = (request: ServerRequest.ServerRequest, response: ServerResp
   }
 
   if (!Cookies.isEmpty(response.cookies)) {
-    const toSet = Cookies.toSetCookieHeaders(response.cookies)
-    for (const header of toSet) {
+    for (const header of Cookies.toSetCookieHeaders(response.cookies)) {
       fields.headers.append("set-cookie", header)
     }
   }
diff --git a/packages/platform-node/test/HttpServer.test.ts b/packages/platform-node/test/HttpServer.test.ts
index 4b7b36de79..bc5eac5e94 100644
--- a/packages/platform-node/test/HttpServer.test.ts
+++ b/packages/platform-node/test/HttpServer.test.ts
@@ -604,20 +604,19 @@ describe("HttpServer", () => {
       const client = yield* _(makeClient)
       const res = yield* _(HttpC.request.get("/home"), client, Effect.scoped)
       assert.deepStrictEqual(
-        res.cookies.cookies[0].toJSON(),
-        Http.cookies.unsafeMakeCookie("test", "value").toJSON()
-      )
-      assert.deepStrictEqual(
-        res.cookies.cookies[1].toJSON(),
-        Http.cookies.unsafeMakeCookie("test2", "value2", {
-          httpOnly: true,
-          secure: true,
-          sameSite: "lax",
-          partitioned: true,
-          path: "/",
-          domain: "example.com",
-          expires: new Date(2022, 1, 1, 0, 0, 0, 0),
-          maxAge: Duration.minutes(5)
+        res.cookies.toJSON(),
+        Http.cookies.fromReadonlyRecord({
+          test: Http.cookies.unsafeMakeCookie("test", "value"),
+          test2: Http.cookies.unsafeMakeCookie("test2", "value2", {
+            httpOnly: true,
+            secure: true,
+            sameSite: "lax",
+            partitioned: true,
+            path: "/",
+            domain: "example.com",
+            expires: new Date(2022, 1, 1, 0, 0, 0, 0),
+            maxAge: Duration.minutes(5)
+          })
         }).toJSON()
       )
     }).pipe(Effect.scoped, runPromise))
diff --git a/packages/platform/src/Http/Cookies.ts b/packages/platform/src/Http/Cookies.ts
index f945628669..bddf8fb200 100644
--- a/packages/platform/src/Http/Cookies.ts
+++ b/packages/platform/src/Http/Cookies.ts
@@ -8,7 +8,7 @@ import * as Inspectable from "effect/Inspectable"
 import * as Option from "effect/Option"
 import { type Pipeable, pipeArguments } from "effect/Pipeable"
 import * as Predicate from "effect/Predicate"
-import * as ReadonlyArray from "effect/ReadonlyArray"
+import * as ReadonlyRecord from "effect/ReadonlyRecord"
 import type * as Types from "effect/Types"
 import { TypeIdError } from "../Error.js"
 
@@ -36,7 +36,7 @@ export const isCookies = (u: unknown): u is Cookies => Predicate.hasProperty(u,
  */
 export interface Cookies extends Pipeable, Inspectable.Inspectable {
   readonly [TypeId]: TypeId
-  readonly cookies: ReadonlyArray<Cookie>
+  readonly cookies: ReadonlyRecord.ReadonlyRecord<string, Cookie>
 }
 
 /**
@@ -103,7 +103,7 @@ const Proto: Omit<Cookies, "cookies"> = {
   toJSON(this: Cookies) {
     return {
       _id: "@effect/platform/Http/Cookies",
-      cookies: this.cookies.map((cookie) => cookie.toJSON())
+      cookies: ReadonlyRecord.map(this.cookies, (cookie) => cookie.toJSON())
     }
   },
   pipe() {
@@ -117,12 +117,26 @@ const Proto: Omit<Cookies, "cookies"> = {
  * @since 1.0.0
  * @category constructors
  */
-export const fromIterable = (cookies: Iterable<Cookie>): Cookies => {
+export const fromReadonlyRecord = (cookies: ReadonlyRecord.ReadonlyRecord<string, Cookie>): Cookies => {
   const self = Object.create(Proto)
-  self.cookies = ReadonlyArray.fromIterable(cookies)
+  self.cookies = cookies
   return self
 }
 
+/**
+ * Create a Cookies object from an Iterable
+ *
+ * @since 1.0.0
+ * @category constructors
+ */
+export const fromIterable = (cookies: Iterable<Cookie>): Cookies => {
+  const record: Record<string, Cookie> = {}
+  for (const cookie of cookies) {
+    record[cookie.name] = cookie
+  }
+  return fromReadonlyRecord(record)
+}
+
 /**
  * Create a Cookies object from a set of Set-Cookie headers
  *
@@ -285,7 +299,7 @@ export const empty: Cookies = fromIterable([])
  * @since 1.0.0
  * @category refinements
  */
-export const isEmpty = (self: Cookies): boolean => self.cookies.length === 0
+export const isEmpty = (self: Cookies): boolean => ReadonlyRecord.isEmptyRecord(self.cookies)
 
 // eslint-disable-next-line no-control-regex
 const fieldContentRegExp = /^[\u0009\u0020-\u007e\u0080-\u00ff]+$/
@@ -362,7 +376,7 @@ export const unsafeMakeCookie = (
  * @since 1.0.0
  * @category combinators
  */
-export const append: {
+export const setCookie: {
   (cookie: Cookie): (self: Cookies) => Cookies
   (
     self: Cookies,
@@ -370,7 +384,12 @@ export const append: {
   ): Cookies
 } = dual(
   2,
-  (self: Cookies, cookie: Cookie) => fromIterable([...self.cookies, cookie])
+  (self: Cookies, cookie: Cookie) =>
+    fromReadonlyRecord(ReadonlyRecord.set(
+      self.cookies,
+      cookie.name,
+      cookie
+    ))
 )
 
 /**
@@ -379,16 +398,19 @@ export const append: {
  * @since 1.0.0
  * @category combinators
  */
-export const appendAll: {
+export const setAllCookie: {
   (cookies: Iterable<Cookie>): (self: Cookies) => Cookies
   (
     self: Cookies,
     cookies: Iterable<Cookie>
   ): Cookies
-} = dual(2, (self: Cookies, cookies: Iterable<Cookie>) =>
-  fromIterable(
-    ReadonlyArray.appendAll(self.cookies, cookies)
-  ))
+} = dual(2, (self: Cookies, cookies: Iterable<Cookie>) => {
+  const record = { ...self.cookies }
+  for (const cookie of cookies) {
+    record[cookie.name] = cookie
+  }
+  return fromReadonlyRecord(record)
+})
 
 /**
  * Combine two Cookies objects, removing duplicates from the first
@@ -402,12 +424,11 @@ export const merge: {
     self: Cookies,
     that: Cookies
   ): Cookies
-} = dual(2, (self: Cookies, that: Cookies) => {
-  const cookies = self.cookies.filter((c) => !that.cookies.some((c2) => c2.name === c.name))
-  // eslint-disable-next-line no-restricted-syntax
-  cookies.push(...that.cookies)
-  return fromIterable(cookies)
-})
+} = dual(2, (self: Cookies, that: Cookies) =>
+  fromReadonlyRecord({
+    ...self.cookies,
+    ...that.cookies
+  }))
 
 /**
  * Remove a cookie by name
@@ -421,10 +442,7 @@ export const remove: {
     self: Cookies,
     name: string
   ): Cookies
-} = dual(2, (self: Cookies, cookie: Cookie) =>
-  fromIterable(
-    self.cookies.filter((c) => c.name !== cookie.name)
-  ))
+} = dual(2, (self: Cookies, name: string) => fromReadonlyRecord(ReadonlyRecord.remove(self.cookies, name)))
 
 /**
  * Add a cookie to a Cookies object
@@ -432,7 +450,7 @@ export const remove: {
  * @since 1.0.0
  * @category combinators
  */
-export const add: {
+export const set: {
   (
     name: string,
     value: string,
@@ -449,7 +467,7 @@ export const add: {
   (self: Cookies, name: string, value: string, options?: Cookie["options"]) =>
     Either.map(
       makeCookie(name, value, options),
-      (cookie) => fromIterable([...self.cookies, cookie])
+      (cookie) => fromReadonlyRecord(ReadonlyRecord.set(self.cookies, name, cookie))
     )
 )
 
@@ -459,7 +477,7 @@ export const add: {
  * @since 1.0.0
  * @category combinators
  */
-export const unsafeAdd: {
+export const unsafeSet: {
   (
     name: string,
     value: string,
@@ -474,7 +492,11 @@ export const unsafeAdd: {
 } = dual(
   (args) => isCookies(args[0]),
   (self: Cookies, name: string, value: string, options?: Cookie["options"]) =>
-    append(self, unsafeMakeCookie(name, value, options))
+    fromReadonlyRecord(ReadonlyRecord.set(
+      self.cookies,
+      name,
+      unsafeMakeCookie(name, value, options)
+    ))
 )
 
 /**
@@ -483,7 +505,7 @@ export const unsafeAdd: {
  * @since 1.0.0
  * @category combinators
  */
-export const addAll: {
+export const setAll: {
   (
     cookies: Iterable<readonly [name: string, value: string, options?: Cookie["options"]]>
   ): (self: Cookies) => Either.Either<Cookies, CookiesError>
@@ -497,15 +519,15 @@ export const addAll: {
     self: Cookies,
     cookies: Iterable<readonly [name: string, value: string, options?: Cookie["options"]]>
   ): Either.Either<Cookies, CookiesError> => {
-    const toAdd: Array<Cookie> = []
+    const record: Record<string, Cookie> = { ...self.cookies }
     for (const [name, value, options] of cookies) {
       const either = makeCookie(name, value, options)
       if (Either.isLeft(either)) {
         return either as Either.Left<CookiesError, never>
       }
-      toAdd.push(either.right)
+      record[name] = either.right
     }
-    return Either.right(appendAll(self, toAdd))
+    return Either.right(fromReadonlyRecord(record))
   }
 )
 
@@ -515,7 +537,7 @@ export const addAll: {
  * @since 1.0.0
  * @category combinators
  */
-export const unsafeAddAll: {
+export const unsafeSetAll: {
   (
     cookies: Iterable<readonly [name: string, value: string, options?: Cookie["options"]]>
   ): (self: Cookies) => Cookies
@@ -528,7 +550,7 @@ export const unsafeAddAll: {
   (
     self: Cookies,
     cookies: Iterable<readonly [name: string, value: string, options?: Cookie["options"]]>
-  ): Cookies => Either.getOrThrow(addAll(self, cookies))
+  ): Cookies => Either.getOrThrow(setAll(self, cookies))
 )
 
 /**
@@ -616,7 +638,7 @@ export function serializeCookie(self: Cookie): string {
  * @category encoding
  */
 export const toCookieHeader = (self: Cookies): string =>
-  self.cookies.map((cookie) => `${cookie.name}=${cookie.valueEncoded}`).join("; ")
+  Object.values(self.cookies).map((cookie) => `${cookie.name}=${cookie.valueEncoded}`).join("; ")
 
 /**
  * To record
@@ -626,8 +648,9 @@ export const toCookieHeader = (self: Cookies): string =>
  */
 export const toRecord = (self: Cookies): Record<string, string> => {
   const record: Record<string, string> = {}
-  for (let index = 0; index < self.cookies.length; index++) {
-    const cookie = self.cookies[index]
+  const cookies = Object.values(self.cookies)
+  for (let index = 0; index < cookies.length; index++) {
+    const cookie = cookies[index]
     record[cookie.name] = cookie.value
   }
   return record
@@ -639,7 +662,7 @@ export const toRecord = (self: Cookies): Record<string, string> => {
  * @since 1.0.0
  * @category encoding
  */
-export const toSetCookieHeaders = (self: Cookies): Array<string> => self.cookies.map(serializeCookie)
+export const toSetCookieHeaders = (self: Cookies): Array<string> => Object.values(self.cookies).map(serializeCookie)
 
 /**
  * Parse a cookie header into a record of key-value pairs
diff --git a/packages/platform/src/internal/http/serverResponse.ts b/packages/platform/src/internal/http/serverResponse.ts
index 517df871d1..85917df2fc 100644
--- a/packages/platform/src/internal/http/serverResponse.ts
+++ b/packages/platform/src/internal/http/serverResponse.ts
@@ -65,6 +65,7 @@ class ServerResponseImpl extends Effectable.StructuralClass<ServerResponse.Serve
       status: this.status,
       statusText: this.statusText,
       headers: this.headers,
+      cookies: this.cookies.toJSON(),
       body: this.body.toJSON()
     }
   }
@@ -322,7 +323,7 @@ export const setCookie = dual<
 >(
   (args) => Cookies.isCookies(args[0]),
   (self, name, value, options) =>
-    Effect.map(Cookies.add(self.cookies, name, value, options), (cookies) =>
+    Effect.map(Cookies.set(self.cookies, name, value, options), (cookies) =>
       new ServerResponseImpl(
         self.status,
         self.statusText,
@@ -352,7 +353,7 @@ export const unsafeSetCookie = dual<
       self.status,
       self.statusText,
       self.headers,
-      Cookies.unsafeAdd(self.cookies, name, value, options),
+      Cookies.unsafeSet(self.cookies, name, value, options),
       self.body
     )
 )
@@ -387,7 +388,7 @@ export const setCookies = dual<
 >(
   2,
   (self, cookies) =>
-    Effect.map(Cookies.addAll(self.cookies, cookies), (cookies) =>
+    Effect.map(Cookies.setAll(self.cookies, cookies), (cookies) =>
       new ServerResponseImpl(
         self.status,
         self.statusText,
@@ -413,7 +414,7 @@ export const unsafeSetCookies = dual<
       self.status,
       self.statusText,
       self.headers,
-      Cookies.unsafeAddAll(self.cookies, cookies),
+      Cookies.unsafeSetAll(self.cookies, cookies),
       self.body
     )
 )
@@ -485,11 +486,18 @@ export const setBody = dual<
 
 /** @internal */
 export const toWeb = (response: ServerResponse.ServerResponse, withoutBody = false): Response => {
+  const headers = new globalThis.Headers(response.headers)
+  if (!Cookies.isEmpty(response.cookies)) {
+    const toAdd = Cookies.toSetCookieHeaders(response.cookies)
+    for (const header of toAdd) {
+      headers.append("set-cookie", header)
+    }
+  }
   if (withoutBody) {
     return new Response(undefined, {
       status: response.status,
       statusText: response.statusText as string,
-      headers: response.headers
+      headers
     })
   }
   const body = response.body
@@ -498,7 +506,7 @@ export const toWeb = (response: ServerResponse.ServerResponse, withoutBody = fal
       return new Response(undefined, {
         status: response.status,
         statusText: response.statusText as string,
-        headers: response.headers
+        headers
       })
     }
     case "Uint8Array":
@@ -506,21 +514,21 @@ export const toWeb = (response: ServerResponse.ServerResponse, withoutBody = fal
       return new Response(body.body as any, {
         status: response.status,
         statusText: response.statusText,
-        headers: response.headers
+        headers
       })
     }
     case "FormData": {
       return new Response(body.formData as any, {
         status: response.status,
         statusText: response.statusText,
-        headers: response.headers
+        headers
       })
     }
     case "Stream": {
       return new Response(Stream.toReadableStream(body.stream), {
         status: response.status,
         statusText: response.statusText,
-        headers: response.headers
+        headers
       })
     }
   }
diff --git a/packages/platform/test/Http/App.test.ts b/packages/platform/test/Http/App.test.ts
index cddb884a5c..213ee9b715 100644
--- a/packages/platform/test/Http/App.test.ts
+++ b/packages/platform/test/Http/App.test.ts
@@ -12,6 +12,23 @@ describe("Http/App", () => {
       })
     })
 
+    test("cookies", async () => {
+      const handler = Http.app.toWebHandler(
+        Http.response.unsafeJson({ foo: "bar" }).pipe(
+          Http.response.unsafeSetCookie("foo", "bar"),
+          Http.response.unsafeSetCookie("test", "123", { secure: true, httpOnly: true, sameSite: "strict" })
+        )
+      )
+      const response = await handler(new Request("http://localhost:3000/"))
+      assert.deepStrictEqual(response.headers.getSetCookie(), [
+        "foo=bar",
+        "test=123; HttpOnly; Secure; SameSite=Strict"
+      ])
+      assert.deepStrictEqual(await response.json(), {
+        foo: "bar"
+      })
+    })
+
     test("stream", async () => {
       const handler = Http.app.toWebHandler(Http.response.stream(Stream.make("foo", "bar").pipe(Stream.encodeText)))
       const response = await handler(new Request("http://localhost:3000/"))