diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 5f5f875..0e878e3 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -76,7 +76,7 @@ jobs:
     - name: Install markdownlint-cli2 dependencies locally
       run: sudo npm install --no-package-lock --production
     - name: Lint with formatters
-      run: node ./markdownlint-cli2 CONTRIBUTING.md README.md
+      run: node ./markdownlint-cli2.mjs CONTRIBUTING.md README.md
 
   lint-dockerfile:
     runs-on: ubuntu-latest
diff --git a/.gitignore b/.gitignore
index f09431b..85f9fcd 100644
--- a/.gitignore
+++ b/.gitignore
@@ -4,5 +4,5 @@ npm-debug.log
 !test/customRules/node_modules
 !test/markdownItPlugins/module/node_modules
 !test/outputFormatters-module/node_modules
-webworker/markdownlint-cli2-webworker.js
-webworker/setImmediate.js
+webworker/markdownlint-cli2-webworker.cjs
+webworker/setImmediate.cjs
diff --git a/eslint.config.mjs b/eslint.config.mjs
index 1bc8300..56b2be9 100644
--- a/eslint.config.mjs
+++ b/eslint.config.mjs
@@ -21,8 +21,8 @@ export default [
   {
     "ignores": [
       "test/*/**",
-      "webworker/markdownlint-cli2-webworker.js",
-      "webworker/setImmediate.js"
+      "webworker/markdownlint-cli2-webworker.cjs",
+      "webworker/setImmediate.cjs"
     ]
   },
   {
@@ -66,11 +66,7 @@ export default [
   {
     "files": [
       "**/*-formatter-*.js",
-      "webworker/*.cjs",
-      "webworker/*.js"
-    ],
-    "ignores": [
-      "webworker/fs-virtual.js"
+      "webworker/*.cjs"
     ],
     "languageOptions": {
       "sourceType": "commonjs",
diff --git a/markdownlint-cli2.mjs b/markdownlint-cli2.mjs
index 0804adf..6ef2c20 100755
--- a/markdownlint-cli2.mjs
+++ b/markdownlint-cli2.mjs
@@ -886,8 +886,8 @@ const outputSummary = async (
     const dirs = [ dir, ...modulePaths ];
     const formattersAndParams = outputFormatters
       ? await importOrRequireIdsAndParams(dirs, outputFormatters, noRequire)
-      // eslint-disable-next-line unicorn/no-await-expression-member
-      : [ [ (await import("markdownlint-cli2-formatter-default")).default ] ];
+      // eslint-disable-next-line no-inline-comments, unicorn/no-await-expression-member
+      : [ [ (await import(/* webpackMode: "eager" */ "markdownlint-cli2-formatter-default")).default ] ];
     await Promise.all(formattersAndParams.map((formatterAndParams) => {
       const [ formatter, ...formatterParams ] = formatterAndParams;
       return formatter(formatterOptions, ...formatterParams);
diff --git a/package.json b/package.json
index 7bd73a9..46e500f 100644
--- a/package.json
+++ b/package.json
@@ -49,7 +49,7 @@
     "test-watch": "git ls-files | entr npm run test",
     "update-snapshots": "ava --timeout=1m --update-snapshots test/markdownlint-cli2-test-exec.mjs test/markdownlint-cli2-test-fs.mjs test/markdownlint-cli2-test-main.mjs",
     "webworker": "cd webworker && webpack --mode none",
-    "webworker-install": "npm install --no-package-lock --no-save path-browserify setimmediate stream-browserify util webpack-cli && cpy ./node_modules/setimmediate/setImmediate.cjs ./webworker --flat"
+    "webworker-install": "npm install --no-package-lock --no-save path-browserify setimmediate stream-browserify util webpack-cli && cpy ./node_modules/setimmediate/setImmediate.js ./webworker/setImmediate.cjs --flat"
   },
   "engines": {
     "node": ">=18"
diff --git a/webworker/index.cjs b/webworker/index.cjs
deleted file mode 100644
index 13cc62c..0000000
--- a/webworker/index.cjs
+++ /dev/null
@@ -1,5 +0,0 @@
-// @ts-check
-
-"use strict";
-
-module.exports = require("../markdownlint-cli2.mjs");
diff --git a/webworker/index.html b/webworker/index.html
index e6f2ec3..93697b1 100644
--- a/webworker/index.html
+++ b/webworker/index.html
@@ -10,9 +10,9 @@
     <div id="qunit"></div>
     <div id="qunit-fixture"></div>
     <script src="https://code.jquery.com/qunit/qunit-2.20.0.js" crossorigin="anonymous" integrity="sha256-qDPbT8viaD6gCaTrUd7FOE5lU5S9H5U5bbuQMADnrRY="></script>
-    <script src="./setImmediate.js"></script>
-    <script src="./markdownlint-cli2-webworker.js"></script>
-    <script src="./fs-virtual.js"></script>
-    <script src="./webworker-test.js"></script>
+    <script src="./setImmediate.cjs"></script>
+    <script src="./markdownlint-cli2-webworker.cjs"></script>
+    <script src="./fs-virtual.cjs"></script>
+    <script src="./webworker-test.cjs"></script>
   </body>
 </html>
diff --git a/webworker/index.mjs b/webworker/index.mjs
new file mode 100644
index 0000000..5abe053
--- /dev/null
+++ b/webworker/index.mjs
@@ -0,0 +1,3 @@
+// @ts-check
+
+export { main } from "../markdownlint-cli2.mjs";
diff --git a/webworker/webpack.config.cjs b/webworker/webpack.config.cjs
index c1ea1e1..336498f 100644
--- a/webworker/webpack.config.cjs
+++ b/webworker/webpack.config.cjs
@@ -7,9 +7,10 @@
 const webpack = require("webpack");
 const nodeModulePrefixRe = /^node:/u;
 
+/** @type {import("webpack").Configuration} */
 module.exports = {
   "target": "webworker",
-  "entry": "./index.js",
+  "entry": "./index.mjs",
   "output": {
     "path": __dirname,
     "filename": "markdownlint-cli2-webworker.cjs",
@@ -31,14 +32,14 @@ module.exports = {
     new webpack.NormalModuleReplacementPlugin(
       /^stream\/(?:consumers|promises)$/u,
       (resource) => {
-        resource.request = require.resolve("./module-empty.js");
+        resource.request = require.resolve("./module-empty.cjs");
       }
     ),
     // Intercept existing "unicorn-magic" package to provide missing import
     new webpack.NormalModuleReplacementPlugin(
       /^unicorn-magic$/u,
       (resource) => {
-        resource.request = require.resolve("./unicorn-magic-stub.js");
+        resource.request = require.resolve("./unicorn-magic-stub.cjs");
       }
     ),
     // Intercept use of "process" to provide implementation
@@ -50,12 +51,13 @@ module.exports = {
     "fallback": {
       "buffer": false,
       "fs": false,
-      "os": require.resolve("./os-stub.js"),
+      "module": false,
+      "os": require.resolve("./os-stub.cjs"),
       "path": require.resolve("path-browserify"),
-      "process": require.resolve("./process-stub.js"),
-      "process-wrapper": require.resolve("./process-stub.js"),
+      "process": require.resolve("./process-stub.cjs"),
+      "process-wrapper": require.resolve("./process-stub.cjs"),
       "stream": require.resolve("stream-browserify"),
-      "url": require.resolve("./module-empty.js")
+      "url": require.resolve("./module-empty.cjs")
     }
   }
 };