diff --git a/async/abortable_test.ts b/async/abortable_test.ts
index 7da8e97806af..c9f3b4254b0e 100644
--- a/async/abortable_test.ts
+++ b/async/abortable_test.ts
@@ -130,7 +130,7 @@ Deno.test("abortable.AsyncIterable() handles already aborted signal", async () =
 Deno.test("abortable.AsyncIterable() calls return before throwing", async () => {
   const c = new AbortController();
   let returnCalled = false;
-  let timeoutId: number;
+  let timeoutId;
   const iterable: AsyncIterable<string> = {
     [Symbol.asyncIterator]: () => ({
       next: () =>
diff --git a/async/unstable_abortable_test.ts b/async/unstable_abortable_test.ts
index 060209877f33..eae51bd9a6e7 100644
--- a/async/unstable_abortable_test.ts
+++ b/async/unstable_abortable_test.ts
@@ -130,7 +130,7 @@ Deno.test("abortable.AsyncIterable() handles already aborted signal", async () =
 Deno.test("abortable.AsyncIterable() calls return before throwing", async () => {
   const c = new AbortController();
   let returnCalled = false;
-  let timeoutId: number;
+  let timeoutId;
   const iterable: AsyncIterable<string> = {
     [Symbol.asyncIterator]: () => ({
       next: () =>
diff --git a/async/unstable_throttle.ts b/async/unstable_throttle.ts
index e68020d925f9..410db695b8bf 100644
--- a/async/unstable_throttle.ts
+++ b/async/unstable_throttle.ts
@@ -106,7 +106,7 @@ export function throttle<T extends Array<any>>(
   options?: ThrottleOptions,
 ): ThrottledFunction<T> {
   const ensureLast = Boolean(options?.ensureLastCall);
-  let timeout = -1;
+  let timeout: ReturnType<typeof setTimeout> | undefined;
 
   let lastExecution = -Infinity;
   let flush: (() => void) | null = null;
diff --git a/async/unstable_wait_for.ts b/async/unstable_wait_for.ts
index 748742426fe9..489cae4a7b4b 100644
--- a/async/unstable_wait_for.ts
+++ b/async/unstable_wait_for.ts
@@ -51,7 +51,7 @@ export function waitFor(
   const { step = 100 } = options;
 
   // Create a new promise that resolves when the predicate is true
-  let timer: number;
+  let timer: ReturnType<typeof setTimeout>;
   const p: Promise<void> = new Promise(function (resolve) {
     const setTimer = () => {
       timer = setTimeout(async () => {
diff --git a/cache/ttl_cache.ts b/cache/ttl_cache.ts
index 7f93795a3642..f0251c1f53ab 100644
--- a/cache/ttl_cache.ts
+++ b/cache/ttl_cache.ts
@@ -93,7 +93,7 @@ export interface TtlCacheOptions<K, V> {
 export class TtlCache<K, V> extends Map<K, V>
   implements MemoizationCache<K, V> {
   #defaultTtl: number;
-  #timeouts = new Map<K, number>();
+  #timeouts = new Map();
   #eject?: ((ejectedKey: K, ejectedValue: V) => void) | undefined;
   #slidingExpiration: boolean;
   #entryTtls?: Map<K, number>;
diff --git a/cli/unstable_progress_bar.ts b/cli/unstable_progress_bar.ts
index 8201561106bd..ea49843a98b6 100644
--- a/cli/unstable_progress_bar.ts
+++ b/cli/unstable_progress_bar.ts
@@ -193,7 +193,7 @@ export class ProgressBar {
   max: number;
 
   #writer: WritableStreamDefaultWriter;
-  #id: number;
+  #id;
   #startTime: number;
   #previousTime: number;
   #previousValue: number;
diff --git a/cli/unstable_spinner.ts b/cli/unstable_spinner.ts
index 095c6be269c6..6e9bbd498eaf 100644
--- a/cli/unstable_spinner.ts
+++ b/cli/unstable_spinner.ts
@@ -139,7 +139,7 @@ export class Spinner {
 
   #interval: number;
   #color: Color | undefined;
-  #intervalId: number | null = null;
+  #intervalId: ReturnType<typeof setInterval> | null = null;
   #output: typeof Deno.stdout | typeof Deno.stderr;
 
   /**
diff --git a/testing/README.md b/testing/README.md
index 2ab30a4e93e5..67714980e955 100644
--- a/testing/README.md
+++ b/testing/README.md
@@ -10,7 +10,7 @@ This package provides utilities for testing.
 import { assertSpyCalls, spy } from "@std/testing/mock";
 import { FakeTime } from "@std/testing/time";
 
-function secondInterval(cb: () => void): number {
+function secondInterval(cb: () => void) {
   return setInterval(cb, 1000);
 }
 
diff --git a/testing/bdd_test.ts b/testing/bdd_test.ts
index df44d5787a68..e5fa4fae317f 100644
--- a/testing/bdd_test.ts
+++ b/testing/bdd_test.ts
@@ -42,7 +42,7 @@ interface GlobalContext {
 }
 
 let timerIdx = 1;
-const timers = new Map<number, number>();
+const timers = new Map();
 function hookFns() {
   timerIdx = 1;
   timers.clear();
diff --git a/testing/mock.ts b/testing/mock.ts
index 71f53944e96e..76a2f53ef203 100644
--- a/testing/mock.ts
+++ b/testing/mock.ts
@@ -293,7 +293,7 @@
  * } from "@std/testing/mock";
  * import { FakeTime } from "@std/testing/time";
  *
- * function secondInterval(cb: () => void): number {
+ * function secondInterval(cb: () => void) {
  *   return setInterval(cb, 1000);
  * }
  *
diff --git a/testing/time.ts b/testing/time.ts
index 7afd02535027..53463e4a3e1a 100644
--- a/testing/time.ts
+++ b/testing/time.ts
@@ -10,7 +10,7 @@
  * } from "@std/testing/mock";
  * import { FakeTime } from "@std/testing/time";
  *
- * function secondInterval(cb: () => void): number {
+ * function secondInterval(cb: () => void) {
  *   return setInterval(cb, 1000);
  * }
  *
@@ -138,15 +138,15 @@ function assertIsCallbackFunction(
   }
 }
 
-const fakeSetTimeout: typeof globalThis.setTimeout = function (
-  callback,
+function fakeSetTimeout(
+  callback: string | ((...args: unknown[]) => unknown),
   delay = 0,
-  ...args
-) {
+  ...args: unknown[]
+): number {
   assertIsCallbackFunction(callback, "setTimeout");
   if (!time) throw new TimeError("Cannot set timeout: time is not faked");
   return setTimer(callback, delay, args, false);
-};
+}
 
 function fakeClearTimeout(id?: unknown) {
   if (!time) throw new TimeError("Cannot clear timeout: time is not faked");
@@ -155,15 +155,15 @@ function fakeClearTimeout(id?: unknown) {
   }
 }
 
-const fakeSetInterval: typeof globalThis.setInterval = function (
-  callback,
+function fakeSetInterval(
+  callback: string | ((...args: unknown[]) => unknown),
   delay = 0,
-  ...args
-) {
+  ...args: unknown[]
+): number {
   assertIsCallbackFunction(callback, "setInterval");
   if (!time) throw new TimeError("Cannot set interval: time is not faked");
   return setTimer(callback, delay, args, true);
-};
+}
 
 function fakeClearInterval(id?: unknown) {
   if (!time) throw new TimeError("Cannot clear interval: time is not faked");
@@ -173,8 +173,7 @@ function fakeClearInterval(id?: unknown) {
 }
 
 function setTimer(
-  // deno-lint-ignore no-explicit-any
-  callback: (...args: any[]) => void,
+  callback: (...args: unknown[]) => unknown,
   delay = 0,
   args: unknown[],
   repeat = false,
@@ -209,9 +208,11 @@ function fakeAbortSignalTimeout(delay: number): AbortSignal {
 
 function overrideGlobals() {
   globalThis.Date = FakeDate;
-  globalThis.setTimeout = fakeSetTimeout;
+  globalThis.setTimeout =
+    fakeSetTimeout as unknown as typeof globalThis.setTimeout;
   globalThis.clearTimeout = fakeClearTimeout;
-  globalThis.setInterval = fakeSetInterval;
+  globalThis.setInterval =
+    fakeSetInterval as unknown as typeof globalThis.setInterval;
   globalThis.clearInterval = fakeClearInterval;
   AbortSignal.timeout = fakeAbortSignalTimeout;
 }
@@ -245,7 +246,7 @@ let now: number;
 let initializedAt: number;
 let advanceRate: number;
 let advanceFrequency: number;
-let advanceIntervalId: number | undefined;
+let advanceIntervalId: ReturnType<typeof setInterval> | undefined;
 let timerId: Generator<number>;
 let dueNodes: Map<number, DueNode>;
 let dueTree: RedBlackTree<DueNode>;
@@ -265,7 +266,7 @@ let dueTree: RedBlackTree<DueNode>;
  * } from "@std/testing/mock";
  * import { FakeTime } from "@std/testing/time";
  *
- * function secondInterval(cb: () => void): number {
+ * function secondInterval(cb: () => void) {
  *   return setInterval(cb, 1000);
  * }
  *
@@ -575,7 +576,7 @@ export class FakeTime {
       );
     }
     return await new Promise((resolve, reject) => {
-      let timer: number | null = null;
+      let timer: ReturnType<typeof setTimeout> | null = null;
       const abort = () =>
         FakeTime
           .restoreFor(() => {
@@ -629,7 +630,7 @@ export class FakeTime {
    * } from "@std/testing/mock";
    * import { FakeTime } from "@std/testing/time";
    *
-   * function secondInterval(cb: () => void): number {
+   * function secondInterval(cb: () => void) {
    *   return setInterval(cb, 1000);
    * }
    *
diff --git a/testing/time_test.ts b/testing/time_test.ts
index 176f27de85fd..8414bbf200e0 100644
--- a/testing/time_test.ts
+++ b/testing/time_test.ts
@@ -163,7 +163,7 @@ Deno.test("FakeTime controls timeouts", () => {
 
   setTimeout(cb, 1000, "a");
   setTimeout(cb, 1500, "b");
-  const timeout: number = setTimeout(cb, 1750, "c");
+  const timeout = setTimeout(cb, 1750, "c");
   setTimeout(cb, 2000, "d");
   time.tick(1250);
   expected.push({ args: ["a"], returned: 7000 });
@@ -199,7 +199,7 @@ Deno.test("FakeTime controls intervals", () => {
   const cb = spy(fromNow());
   const expected: SpyCall[] = [];
 
-  const interval: number = setInterval(cb, 1000);
+  const interval = setInterval(cb, 1000);
   time.tick(250);
   assertEquals(cb.calls, expected);
   time.tick(250);
@@ -226,7 +226,7 @@ Deno.test("FakeTime calls timeout and interval callbacks in correct order", () =
   const timeoutExpected: SpyCall[] = [];
   const intervalExpected: SpyCall[] = [];
 
-  const interval: number = setInterval(intervalCb, 1000);
+  const interval = setInterval(intervalCb, 1000);
   setTimeout(timeoutCb, 500);
   time.tick(250);
   assertEquals(intervalCb.calls, intervalExpected);
diff --git a/toml/_parser_test.ts b/toml/_parser_test.ts
index efa569984e99..a91ea0a614ca 100644
--- a/toml/_parser_test.ts
+++ b/toml/_parser_test.ts
@@ -489,7 +489,7 @@ Deno.test({
 Deno.test({
   name: "(private) deepAssign() works correctly",
   fn() {
-    const source = {
+    const source: Record<string, unknown> = {
       foo: {
         items: [
           {
@@ -528,7 +528,7 @@ Deno.test({
                 email: {
                   x: { main: "mail@example.com" },
                 },
-              } as unknown,
+              },
             },
           ],
         },