diff --git a/bytes/last_index_of_needle.ts b/bytes/last_index_of_needle.ts
index d4f3c00ae4ad..952670802340 100644
--- a/bytes/last_index_of_needle.ts
+++ b/bytes/last_index_of_needle.ts
@@ -20,7 +20,7 @@
 export function lastIndexOfNeedle(
   source: Uint8Array,
   needle: Uint8Array,
-  start = source.length - 1,
+  start: number = source.length - 1,
 ): number {
   if (start < 0) {
     return -1;
diff --git a/http/unstable_cookie_map.ts b/http/unstable_cookie_map.ts
index baef5f0a26e9..63341c36115e 100644
--- a/http/unstable_cookie_map.ts
+++ b/http/unstable_cookie_map.ts
@@ -370,7 +370,7 @@ const keys = Symbol("#keys");
 const requestHeaders = Symbol("#requestHeaders");
 const responseHeaders = Symbol("#responseHeaders");
 const isSecure = Symbol("#secure");
-const requestKeys = Symbol("#requestKeys");
+const requestKeys: unique symbol = Symbol("#requestKeys");
 
 /** An internal abstract class which provides common functionality for
  * {@link CookieMap} and {@link SecureCookieMap}.
@@ -417,7 +417,7 @@ abstract class CookieMapBase implements Mergeable {
     return init;
   }
 
-  [Symbol.for("Deno.customInspect")]() {
+  [Symbol.for("Deno.customInspect")](): string {
     return `${this.constructor.name} []`;
   }
 
@@ -426,7 +426,7 @@ abstract class CookieMapBase implements Mergeable {
     // deno-lint-ignore no-explicit-any
     options: any,
     inspect: (value: unknown, options?: unknown) => string,
-  ) {
+  ): string {
     if (depth < 0) {
       return options.stylize(`[${this.constructor.name}]`, "special");
     }
diff --git a/io/slice_long_to_bytes.ts b/io/slice_long_to_bytes.ts
index a832d3cbed91..61dfbd41a59b 100644
--- a/io/slice_long_to_bytes.ts
+++ b/io/slice_long_to_bytes.ts
@@ -10,7 +10,7 @@
  */
 export function sliceLongToBytes(
   d: number,
-  dest = Array.from<number>({ length: 8 }),
+  dest: number[] = Array.from<number>({ length: 8 }),
 ): number[] {
   let big = BigInt(d);
   for (let i = 0; i < 8; i++) {
diff --git a/log/handlers.ts b/log/handlers.ts
index ef04989ca4fe..7837a0919415 100644
--- a/log/handlers.ts
+++ b/log/handlers.ts
@@ -143,7 +143,7 @@ export class FileHandler extends WriterHandler {
   protected _filename: string;
   protected _mode: LogMode;
   protected _openOptions: Deno.OpenOptions;
-  protected _encoder = new TextEncoder();
+  protected _encoder: TextEncoder = new TextEncoder();
   #unloadCallback = (() => {
     this.destroy();
   }).bind(this);
diff --git a/log/mod.ts b/log/mod.ts
index d5ebb38d0849..3bafde5cedfe 100644
--- a/log/mod.ts
+++ b/log/mod.ts
@@ -357,7 +357,7 @@
  */
 
 import { Logger } from "./logger.ts";
-import type { GenericFunction } from "./logger.ts";
+import type { GenericFunction, LogRecord } from "./logger.ts";
 import {
   BaseHandler,
   ConsoleHandler,
@@ -439,7 +439,9 @@ export const handlers = {
   RotatingFileHandler,
 };
 
-export const formatters = {
+export const formatters: {
+  jsonFormatter(logRecord: LogRecord): string;
+} = {
   jsonFormatter,
 };
 
diff --git a/path/common.ts b/path/common.ts
index 5ac90e93c396..449ebaf309fc 100644
--- a/path/common.ts
+++ b/path/common.ts
@@ -16,6 +16,6 @@ import { SEP } from "./separator.ts";
  *       console.log(p); // "./deno/std/"
  * ```
  */
-export function common(paths: string[], sep = SEP): string {
+export function common(paths: string[], sep: typeof SEP = SEP): string {
   return _common(paths, sep);
 }
diff --git a/path/posix/common.ts b/path/posix/common.ts
index ae1bc581e562..5acbbd70658d 100644
--- a/path/posix/common.ts
+++ b/path/posix/common.ts
@@ -16,6 +16,6 @@ import { SEP } from "./separator.ts";
  *       console.log(p); // "./deno/std/"
  * ```
  */
-export function common(paths: string[], sep = SEP): string {
+export function common(paths: string[], sep: typeof SEP = SEP): string {
   return _common(paths, sep);
 }
diff --git a/path/windows/common.ts b/path/windows/common.ts
index ae1bc581e562..5acbbd70658d 100644
--- a/path/windows/common.ts
+++ b/path/windows/common.ts
@@ -16,6 +16,6 @@ import { SEP } from "./separator.ts";
  *       console.log(p); // "./deno/std/"
  * ```
  */
-export function common(paths: string[], sep = SEP): string {
+export function common(paths: string[], sep: typeof SEP = SEP): string {
   return _common(paths, sep);
 }
diff --git a/streams/byte_slice_stream.ts b/streams/byte_slice_stream.ts
index 994d580d0647..4e7e7a4180c5 100644
--- a/streams/byte_slice_stream.ts
+++ b/streams/byte_slice_stream.ts
@@ -21,7 +21,7 @@ export class ByteSliceStream extends TransformStream<Uint8Array, Uint8Array> {
   #offsetEnd = 0;
 
   /** Constructs a new instance. */
-  constructor(start = 0, end = Infinity) {
+  constructor(start = 0, end: number = Infinity) {
     super({
       start: () => {
         assert(start >= 0, "`start` must be greater than 0");
diff --git a/yaml/schema/core.ts b/yaml/schema/core.ts
index c8674e6292e6..59e8e9d40c8e 100644
--- a/yaml/schema/core.ts
+++ b/yaml/schema/core.ts
@@ -9,6 +9,6 @@ import { json } from "./json.ts";
 
 // Standard YAML's Core schema.
 // http://www.yaml.org/spec/1.2/spec.html#id2804923
-export const core = new Schema({
+export const core: Schema = new Schema({
   include: [json],
 });
diff --git a/yaml/schema/default.ts b/yaml/schema/default.ts
index 32e9741f0694..909173bb514f 100644
--- a/yaml/schema/default.ts
+++ b/yaml/schema/default.ts
@@ -10,7 +10,7 @@ import { core } from "./core.ts";
 
 // JS-YAML's default schema for `safeLoad` function.
 // It is not described in the YAML specification.
-export const def = new Schema({
+export const def: Schema = new Schema({
   explicit: [binary, omap, pairs, set],
   implicit: [timestamp, merge],
   include: [core],
diff --git a/yaml/schema/extended.ts b/yaml/schema/extended.ts
index 5526c6119489..83452269edae 100644
--- a/yaml/schema/extended.ts
+++ b/yaml/schema/extended.ts
@@ -33,7 +33,7 @@ import { def } from "./default.ts";
  * );
  * ```
  */
-export const extended = new Schema({
+export const extended: Schema = new Schema({
   explicit: [regexp, undefinedType],
   include: [def],
 });
diff --git a/yaml/schema/failsafe.ts b/yaml/schema/failsafe.ts
index 62c310a69923..bcfa5a4ea210 100644
--- a/yaml/schema/failsafe.ts
+++ b/yaml/schema/failsafe.ts
@@ -9,6 +9,6 @@ import { map, seq, str } from "../_type/mod.ts";
 
 // Standard YAML's Failsafe schema.
 // http://www.yaml.org/spec/1.2/spec.html#id2802346
-export const failsafe = new Schema({
+export const failsafe: Schema = new Schema({
   explicit: [str, seq, map],
 });
diff --git a/yaml/schema/json.ts b/yaml/schema/json.ts
index 73df97c91186..68a147c9984f 100644
--- a/yaml/schema/json.ts
+++ b/yaml/schema/json.ts
@@ -10,7 +10,7 @@ import { failsafe } from "./failsafe.ts";
 
 // Standard YAML's JSON schema.
 // http://www.yaml.org/spec/1.2/spec.html#id2803231
-export const json = new Schema({
+export const json: Schema = new Schema({
   implicit: [nil, bool, int, float],
   include: [failsafe],
 });