diff --git a/.gitignore b/.gitignore
index bb63c80db..1ab4d9d63 100644
--- a/.gitignore
+++ b/.gitignore
@@ -279,10 +279,9 @@ __pycache__/
 # !tools/packages.config
 
 generated/
-lib/
 inputfiles/browser.webidl.json
 .vscode/*
 !.vscode/launch.template.json
 yarn.lock
 TypeScript
-deploy/generated
\ No newline at end of file
+deploy/generated
diff --git a/deploy/deployChangedPackages.js b/deploy/deployChangedPackages.js
index 9d5348fca..e18ad2236 100644
--- a/deploy/deployChangedPackages.js
+++ b/deploy/deployChangedPackages.js
@@ -10,7 +10,7 @@ import * as path from "path";
 import { spawnSync } from "child_process";
 import { Octokit } from "@octokit/rest";
 import { printUnifiedDiff } from "print-diff";
-import { generateChangelogFrom } from "../lib/changelog.js";
+import { generateChangelogFrom } from "../src/changelog.ts";
 import { packages } from "./createTypesPackages.js";
 import { fileURLToPath } from "node:url";
 import fetch from "node-fetch";
diff --git a/deploy/jsconfig.json b/deploy/jsconfig.json
index ab435e545..65199e820 100644
--- a/deploy/jsconfig.json
+++ b/deploy/jsconfig.json
@@ -4,6 +4,7 @@
     "module": "esnext", // es2022
     "moduleResolution": "node",
     "strict": true,
-    "resolveJsonModule": true
+    "resolveJsonModule": true,
+    "allowImportingTsExtensions": true
   }
 }
diff --git a/deploy/versionChangelog.js b/deploy/versionChangelog.js
index c481af071..eaa9d233f 100644
--- a/deploy/versionChangelog.js
+++ b/deploy/versionChangelog.js
@@ -2,7 +2,7 @@
 
 // npm run ts-changelog @types/web 0.0.1 0.0.3
 
-import { gitShowFile, generateChangelogFrom } from "../lib/changelog.js";
+import { gitShowFile, generateChangelogFrom } from "../src/changelog.ts";
 import { packages } from "./createTypesPackages.js";
 import { basename } from "path";
 
diff --git a/package-lock.json b/package-lock.json
index 37e78a63f..5e75c8bab 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -38,6 +38,9 @@
         "typescript": "^5.9.2",
         "typescript-eslint": "^8",
         "webidl2": "^24.5.0"
+      },
+      "engines": {
+        "node": ">= 22.18.0"
       }
     },
     "node_modules/@aashutoshrathi/word-wrap": {
diff --git a/package.json b/package.json
index a1e1ef0bb..0f240adc0 100644
--- a/package.json
+++ b/package.json
@@ -2,6 +2,9 @@
   "name": "@typescript/dom-lib-generator",
   "version": "0.0.1",
   "private": true,
+  "engines": {
+    "node": ">= 22.18.0"
+  },
   "description": "Provides TypeScript types for the latest web APIs.",
   "keywords": [
     "typescript",
@@ -12,15 +15,15 @@
     "worklet"
   ],
   "scripts": {
-    "build": "tsc && node ./lib/build.js",
+    "build": "node ./src/build.ts",
     "baseline-accept": "cpx \"generated\\**\" baselines\\",
     "lint": "eslint --max-warnings 0 src deploy/*.js scripts && tsc -p deploy/jsconfig.json",
     "lint-fix": "eslint --max-warnings 0 src deploy/*.js scripts --fix",
-    "test": "npm run build && npm run lint && node ./lib/test.js && node ./unittests/index.js",
-    "changelog": "tsc && node ./lib/changelog.js",
+    "test": "npm run build && npm run lint && node ./src/test.ts && node ./unittests/index.js",
+    "changelog": "node ./src/changelog.ts",
     "ts-changelog": "node ./deploy/versionChangelog.js",
     "migrate": "node ./deploy/migrate.js",
-    "version": "npm i && tsc && node ./lib/version.js",
+    "version": "npm i && node ./src/version.ts",
     "generate": "npm run build && npm run baseline-accept"
   },
   "author": {
diff --git a/src/build.ts b/src/build.ts
index 1b1be02ff..166971680 100644
--- a/src/build.ts
+++ b/src/build.ts
@@ -1,20 +1,20 @@
-import * as Browser from "./build/types.js";
+import type * as Browser from "./build/types.ts";
 import { promises as fs } from "fs";
-import { merge, resolveExposure, arrayToMap } from "./build/helpers.js";
-import { type CompilerBehavior, emitWebIdl } from "./build/emitter.js";
-import { convert } from "./build/widlprocess.js";
-import { getExposedTypes } from "./build/expose.js";
+import { merge, resolveExposure, arrayToMap } from "./build/helpers.ts";
+import { type CompilerBehavior, emitWebIdl } from "./build/emitter.ts";
+import { convert } from "./build/widlprocess.ts";
+import { getExposedTypes } from "./build/expose.ts";
 import {
   getDeprecationData,
   getDocsData,
   getRemovalData,
-} from "./build/bcd.js";
-import { getInterfaceElementMergeData } from "./build/webref/elements.js";
-import { getInterfaceToEventMap } from "./build/webref/events.js";
-import { getWebidls } from "./build/webref/idl.js";
+} from "./build/bcd.ts";
+import { getInterfaceElementMergeData } from "./build/webref/elements.ts";
+import { getInterfaceToEventMap } from "./build/webref/events.ts";
+import { getWebidls } from "./build/webref/idl.ts";
 import jsonc from "jsonc-parser";
-import { generateDescriptions } from "./build/mdn-comments.js";
-import readPatches from "./build/patches.js";
+import { generateDescriptions } from "./build/mdn-comments.ts";
+import readPatches from "./build/patches.ts";
 
 function mergeNamesakes(filtered: Browser.WebIdl) {
   const targets = [
diff --git a/src/build/bcd.ts b/src/build/bcd.ts
index c54ceac85..1822fd42a 100644
--- a/src/build/bcd.ts
+++ b/src/build/bcd.ts
@@ -1,12 +1,12 @@
-import * as Browser from "./types.js";
-import {
+import * as Browser from "./types.ts";
+import type {
   CompatStatement,
   SimpleSupportStatement,
   SupportBlock,
 } from "@mdn/browser-compat-data/types";
-import { forceKeepAlive } from "./bcd/keep-alive.js";
-import { mapToBcdCompat } from "./bcd/mapper.js";
-import { hasStableImplementation } from "./bcd/stable.js";
+import { forceKeepAlive } from "./bcd/keep-alive.ts";
+import { mapToBcdCompat } from "./bcd/mapper.ts";
+import { hasStableImplementation } from "./bcd/stable.ts";
 
 function hasMultipleImplementations(support: SupportBlock, prefix?: string) {
   const hasStableImpl = (
diff --git a/src/build/bcd/mapper.ts b/src/build/bcd/mapper.ts
index 1238cd684..1c75c91dc 100644
--- a/src/build/bcd/mapper.ts
+++ b/src/build/bcd/mapper.ts
@@ -1,14 +1,14 @@
-import {
+import type {
   BrowserName,
   CompatStatement,
   Identifier,
   SimpleSupportStatement,
 } from "bcd-idl-mapper";
 import api from "bcd-idl-mapper";
-import * as Browser from "../types.js";
-import { filterMapRecord, isEmptyRecord } from "../utils/record.js";
-import { mapDefined } from "../helpers.js";
-import { hasStableImplementation } from "./stable.js";
+import type * as Browser from "../types.ts";
+import { filterMapRecord, isEmptyRecord } from "../utils/record.ts";
+import { mapDefined } from "../helpers.ts";
+import { hasStableImplementation } from "./stable.ts";
 
 interface DataToMap {
   key: string;
diff --git a/src/build/bcd/stable.ts b/src/build/bcd/stable.ts
index 759448bc9..50bd31c74 100644
--- a/src/build/bcd/stable.ts
+++ b/src/build/bcd/stable.ts
@@ -1,4 +1,4 @@
-import { SimpleSupportStatement } from "@mdn/browser-compat-data/types";
+import type { SimpleSupportStatement } from "@mdn/browser-compat-data/types";
 
 export function hasStableImplementation(
   browser: SimpleSupportStatement | SimpleSupportStatement[] | undefined,
diff --git a/src/build/emitter.ts b/src/build/emitter.ts
index 000a4fe7f..d09597bdc 100644
--- a/src/build/emitter.ts
+++ b/src/build/emitter.ts
@@ -1,4 +1,4 @@
-import * as Browser from "./types.js";
+import * as Browser from "./types.ts";
 import {
   mapToArray,
   distinct,
@@ -10,15 +10,11 @@ import {
   baseTypeConversionMap,
   assertUnique,
   arrayBufferViewTypes,
-} from "./helpers.js";
-import { collectLegacyNamespaceTypes } from "./legacy-namespace.js";
+} from "./helpers.ts";
+import { collectLegacyNamespaceTypes } from "./legacy-namespace.ts";
 
 /// Decide which members of a function to emit
-enum EmitScope {
-  StaticOnly,
-  InstanceOnly,
-  All,
-}
+type EmitScope = "StaticOnly" | "InstanceOnly" | "All";
 
 const tsKeywords = new Set(["default", "delete", "continue"]);
 const extendConflictsBaseTypes: Record<
@@ -38,9 +34,7 @@ const namespacesAsInterfaces = ["console"];
 // Used to decide if a member should be emitted given its static property and
 // the intended scope level.
 function matchScope(scope: EmitScope, x: { static?: boolean }) {
-  return (
-    scope === EmitScope.All || (scope === EmitScope.StaticOnly) === !!x.static
-  );
+  return scope === "All" || (scope === "StaticOnly") === !!x.static;
 }
 
 /// Parameter cannot be named "default" in JavaScript/Typescript so we need to rename it.
@@ -900,7 +894,7 @@ export function emitWebIdl(
     if (
       p.name === "name" &&
       i.name === "Window" &&
-      emitScope === EmitScope.InstanceOnly &&
+      emitScope === "InstanceOnly" &&
       prefix === "declare var "
     ) {
       printer.printLine("/** @deprecated */");
@@ -1114,7 +1108,7 @@ export function emitWebIdl(
         .sort(compareName)
         .forEach((m) => emitMethod(prefix, m, conflictedMembers));
     }
-    if (i.anonymousMethods && emitScope === EmitScope.InstanceOnly) {
+    if (i.anonymousMethods && emitScope === "InstanceOnly") {
       const stringifier = i.anonymousMethods.method.find((m) => m.stringifier);
       if (stringifier) {
         printer.printLine("toString(): string;");
@@ -1163,7 +1157,7 @@ export function emitWebIdl(
       ? "declare function "
       : "";
     emitMethods(methodPrefix, emitScope, i, conflictedMembers);
-    if (emitScope === EmitScope.InstanceOnly) {
+    if (emitScope === "InstanceOnly") {
       emitIteratorForEach(i);
     }
   }
@@ -1171,7 +1165,7 @@ export function emitWebIdl(
   /// Emit all members of every interfaces at the root level.
   /// Called only once on the global polluter object
   function emitAllMembers(i: Browser.Interface) {
-    emitMembers(/*prefix*/ "declare var ", EmitScope.InstanceOnly, i);
+    emitMembers(/*prefix*/ "declare var ", "InstanceOnly", i);
 
     for (const relatedIName of iNameToIDependList[i.name]) {
       const i = allInterfacesMap[relatedIName];
@@ -1275,7 +1269,7 @@ export function emitWebIdl(
         emitConstants(parent);
       }
     }
-    emitMembers(/*prefix*/ "", EmitScope.StaticOnly, i);
+    emitMembers(/*prefix*/ "", "StaticOnly", i);
 
     printer.decreaseIndent();
     printer.printLine("};");
@@ -1493,10 +1487,10 @@ export function emitWebIdl(
     emitInterfaceDeclaration(i);
     printer.increaseIndent();
 
-    emitMembers(/*prefix*/ "", EmitScope.InstanceOnly, i);
+    emitMembers(/*prefix*/ "", "InstanceOnly", i);
     emitConstants(i);
     emitEventHandlers(/*prefix*/ "", i);
-    emitIndexers(EmitScope.InstanceOnly, i);
+    emitIndexers("InstanceOnly", i);
 
     printer.decreaseIndent();
     printer.printLine("}");
@@ -1556,8 +1550,8 @@ export function emitWebIdl(
       namespace.nested.typedefs.sort(compareName).forEach(emitTypeDef);
     }
 
-    emitProperties("var ", EmitScope.InstanceOnly, namespace);
-    emitMethods("function ", EmitScope.InstanceOnly, namespace, new Set());
+    emitProperties("var ", "InstanceOnly", namespace);
+    emitMethods("function ", "InstanceOnly", namespace, new Set());
 
     printer.decreaseIndent();
     printer.printLine("}");
diff --git a/src/build/expose.ts b/src/build/expose.ts
index f2a6098bf..09c7d2345 100644
--- a/src/build/expose.ts
+++ b/src/build/expose.ts
@@ -1,4 +1,4 @@
-import * as Browser from "./types.js";
+import * as Browser from "./types.ts";
 import {
   getEmptyWebIDL,
   deepFilter,
@@ -7,8 +7,8 @@ import {
   filterProperties,
   mapToArray,
   arrayToMap,
-} from "./helpers.js";
-import { isEmptyRecord } from "./utils/record.js";
+} from "./helpers.ts";
+import { isEmptyRecord } from "./utils/record.ts";
 
 class LoggedSet extends Set<string> {
   private unvisited: Set<string>;
diff --git a/src/build/helpers.ts b/src/build/helpers.ts
index da84f2d91..4a211d4ae 100644
--- a/src/build/helpers.ts
+++ b/src/build/helpers.ts
@@ -1,4 +1,4 @@
-import * as Browser from "./types.js";
+import * as Browser from "./types.ts";
 
 // Extended types used but not defined in the spec
 export const arrayBufferViewTypes = new Set([
diff --git a/src/build/legacy-namespace.ts b/src/build/legacy-namespace.ts
index 6000ae6c8..c4652262c 100644
--- a/src/build/legacy-namespace.ts
+++ b/src/build/legacy-namespace.ts
@@ -1,5 +1,5 @@
-import * as Browser from "./types.js";
-import { mapToArray, arrayToMap } from "./helpers.js";
+import * as Browser from "./types.ts";
+import { mapToArray, arrayToMap } from "./helpers.ts";
 
 export function collectLegacyNamespaceTypes(
   webidl: Browser.WebIdl,
diff --git a/src/build/mdn-comments.ts b/src/build/mdn-comments.ts
index a69fa013c..654973856 100644
--- a/src/build/mdn-comments.ts
+++ b/src/build/mdn-comments.ts
@@ -1,5 +1,5 @@
 import { readFile } from "fs/promises";
-import { hyphenToCamelCase } from "./utils/css.js";
+import { hyphenToCamelCase } from "./utils/css.ts";
 
 const inputFile = new URL("../../inputfiles/mdn.json", import.meta.url);
 
diff --git a/src/build/patches.ts b/src/build/patches.ts
index 26368e585..7733a5f61 100644
--- a/src/build/patches.ts
+++ b/src/build/patches.ts
@@ -1,4 +1,4 @@
-import { parse, type Value, type Node, Document } from "kdljs";
+import { parse, type Value, type Node, type Document } from "kdljs";
 import type {
   Enum,
   Event,
@@ -11,9 +11,9 @@ import type {
   Dictionary,
   Member,
   Signature,
-} from "./types.js";
+} from "./types.ts";
 import { readdir, readFile } from "fs/promises";
-import { merge } from "./helpers.js";
+import { merge } from "./helpers.ts";
 
 type DeepPartial<T> = T extends object
   ? { [K in keyof T]?: DeepPartial<T[K]> }
diff --git a/src/build/webref/css.ts b/src/build/webref/css.ts
index 0042e0315..d43e7f5c9 100644
--- a/src/build/webref/css.ts
+++ b/src/build/webref/css.ts
@@ -1,4 +1,4 @@
-import { hyphenToCamelCase } from "../utils/css.js";
+import { hyphenToCamelCase } from "../utils/css.ts";
 
 export function generateWebIdlFromCssProperties(properties: string[]): string {
   return `partial interface CSSStyleProperties {${properties
diff --git a/src/build/webref/elements.ts b/src/build/webref/elements.ts
index 7e2b6ed44..cb19074aa 100644
--- a/src/build/webref/elements.ts
+++ b/src/build/webref/elements.ts
@@ -1,6 +1,6 @@
-import { listAll, Element as WebrefElement } from "@webref/elements";
-import { Interface, WebIdl } from "../types.js";
-import { addToArrayMap } from "../utils/map.js";
+import { listAll, type Element as WebrefElement } from "@webref/elements";
+import type { Interface, WebIdl } from "../types.ts";
+import { addToArrayMap } from "../utils/map.ts";
 
 async function getInterfaceToElementMap(): Promise<
   Map<string, WebrefElement[]>
diff --git a/src/build/webref/events.ts b/src/build/webref/events.ts
index f79895105..5c27951a7 100644
--- a/src/build/webref/events.ts
+++ b/src/build/webref/events.ts
@@ -1,5 +1,5 @@
 import { listAll } from "@webref/events";
-import { addToNestedMap } from "../utils/map.js";
+import { addToNestedMap } from "../utils/map.ts";
 
 export async function getInterfaceToEventMap(): Promise<
   Map<string, Map<string, string>>
diff --git a/src/build/webref/idl.ts b/src/build/webref/idl.ts
index 55a1c27f0..5896705ff 100644
--- a/src/build/webref/idl.ts
+++ b/src/build/webref/idl.ts
@@ -1,6 +1,6 @@
 import { listAll as listAllIdl } from "@webref/idl";
 import { listAll as listAllCss } from "@webref/css";
-import { generateWebIdlFromCssProperties } from "./css.js";
+import { generateWebIdlFromCssProperties } from "./css.ts";
 
 export async function getWebidls(): Promise<Map<string, string>> {
   const idl = await listAllIdl();
diff --git a/src/build/widlprocess.ts b/src/build/widlprocess.ts
index b7fc1c5e6..d8b5ddeb2 100644
--- a/src/build/widlprocess.ts
+++ b/src/build/widlprocess.ts
@@ -1,6 +1,6 @@
 import * as webidl2 from "webidl2";
-import * as Browser from "./types.js";
-import { getEmptyWebIDL } from "./helpers.js";
+import * as Browser from "./types.ts";
+import { getEmptyWebIDL } from "./helpers.ts";
 
 export function convert(text: string, commentMap: Record<string, string>) {
   const rootTypes = webidl2.parse(text);
diff --git a/src/version.ts b/src/version.ts
index 261f14a4e..38a25d061 100644
--- a/src/version.ts
+++ b/src/version.ts
@@ -1,6 +1,6 @@
 import { execSync } from "child_process";
 import { readFile, writeFile } from "fs/promises";
-import { generateDefaultFromRecentTag } from "./changelog.js";
+import { generateDefaultFromRecentTag } from "./changelog.ts";
 
 const output = generateDefaultFromRecentTag();
 
diff --git a/tsconfig.json b/tsconfig.json
index 250d50e58..203e88dd5 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -1,17 +1,17 @@
 {
-    "compilerOptions": {
-        "target": "es2022",
-        "module": "nodenext",
-        "moduleResolution": "nodenext",
-        "outDir": "./lib",
-        "strict": true,
-        "esModuleInterop": true,
-        "sourceMap": true,
-        "noUnusedLocals": true,
-        "noUnusedParameters": true,
-        "resolveJsonModule": true
-    },
-    "include": [
-        "./src"
-    ]
+  "compilerOptions": {
+    "target": "es2022",
+    "module": "nodenext",
+    "moduleResolution": "nodenext",
+    "outDir": "./lib",
+    "strict": true,
+    "esModuleInterop": true,
+    "sourceMap": true,
+    "noUnusedLocals": true,
+    "noUnusedParameters": true,
+    "resolveJsonModule": true,
+    "allowImportingTsExtensions": true,
+    "noEmit": true,
+  },
+  "include": ["./src"],
 }