diff --git a/dwds/debug_extension_mv3/.gitignore b/dwds/debug_extension_mv3/.gitignore
new file mode 100644
index 000000000..4878cbe8b
--- /dev/null
+++ b/dwds/debug_extension_mv3/.gitignore
@@ -0,0 +1,3 @@
+build/
+compiled/
+extension_key.txt
diff --git a/dwds/debug_extension_mv3/build.yaml b/dwds/debug_extension_mv3/build.yaml
new file mode 100644
index 000000000..cdffb3aa9
--- /dev/null
+++ b/dwds/debug_extension_mv3/build.yaml
@@ -0,0 +1,26 @@
+targets:
+  $default:
+    builders:
+      build_web_compilers|entrypoint:
+        options:
+          dart2js_args:
+            - -O1 # Note: Change to -04 for minified JS. 
+            - --csp
+        generate_for:
+          - web/**.dart
+      mv3_extension|client_js_copy_builder:
+        enabled: true
+      
+builders:
+  client_js_copy_builder:
+    import: "tool/copy_builder.dart"
+    builder_factories:
+        - copyBuilder
+    build_extensions:
+      {
+        "web/{{}}.dart.js": ["compiled/{{}}.dart.js"],
+        "web/{{}}.png": ["compiled/{{}}.png"],
+        "web/manifest.json": ["compiled/manifest.json"],
+      }
+    auto_apply: none
+    build_to: source
diff --git a/dwds/debug_extension_mv3/pubspec.yaml b/dwds/debug_extension_mv3/pubspec.yaml
new file mode 100644
index 000000000..b94ad1564
--- /dev/null
+++ b/dwds/debug_extension_mv3/pubspec.yaml
@@ -0,0 +1,17 @@
+name: mv3_extension
+publish_to: none
+version: 1.30.0
+homepage: https://github.com/dart-lang/webdev
+description: >-
+  A Chrome extension for Dart debugging.
+
+environment:
+  sdk: '>=2.12.0 <3.0.0'
+
+dependencies:
+  js: ^0.6.1+1
+
+dev_dependencies:
+  build: ^2.0.0
+  build_web_compilers: ^3.0.0
+  build_runner: ^2.0.6
diff --git a/dwds/debug_extension_mv3/tool/build_extension.sh b/dwds/debug_extension_mv3/tool/build_extension.sh
new file mode 100755
index 000000000..4600bb4b4
--- /dev/null
+++ b/dwds/debug_extension_mv3/tool/build_extension.sh
@@ -0,0 +1,20 @@
+#!/bin/bash
+
+# Copyright 2022 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+# INSTRUCTIONS:
+
+# Builds the unminifed dart2js app (see DDC issue: https://github.com/dart-lang/sdk/issues/49869):
+# ./tool/build_extension.sh
+
+echo "~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~"
+echo "Building dart2js-compiled extension to /compiled directory."
+echo "~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~"
+dart run build_runner build web --output build --release
+
+echo "~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~"
+echo "Updating manifest.json in /compiled directory."
+echo "~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~"
+dart tool/update_dev_files.dart
diff --git a/dwds/debug_extension_mv3/tool/copy_builder.dart b/dwds/debug_extension_mv3/tool/copy_builder.dart
new file mode 100644
index 000000000..07a0c79ab
--- /dev/null
+++ b/dwds/debug_extension_mv3/tool/copy_builder.dart
@@ -0,0 +1,40 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:build/build.dart';
+
+/// Factory for the build script.
+Builder copyBuilder(_) => _CopyBuilder();
+
+class _CopyBuilder extends Builder {
+  @override
+  Map<String, List<String>> get buildExtensions => {
+        "web/{{}}.dart.js": ["compiled/{{}}.dart.js"],
+        "web/{{}}.png": ["compiled/{{}}.png"],
+        "web/manifest.json": ["compiled/manifest.json"],
+      };
+
+  @override
+  void build(BuildStep buildStep) async {
+    final inputAsset = buildStep.inputId;
+    final allowedOutputs = buildStep.allowedOutputs;
+
+    if (allowedOutputs.length != 1) {
+      return;
+    }
+
+    final outputAsset = allowedOutputs.first;
+    await _copyBinaryFile(buildStep,
+        inputAsset: inputAsset, outputAsset: outputAsset);
+  }
+
+  Future<void> _copyBinaryFile(
+    BuildStep buildStep, {
+    required AssetId inputAsset,
+    required AssetId outputAsset,
+  }) {
+    return buildStep.writeAsBytes(
+        outputAsset, buildStep.readAsBytes(inputAsset));
+  }
+}
diff --git a/dwds/debug_extension_mv3/tool/update_dev_files.dart b/dwds/debug_extension_mv3/tool/update_dev_files.dart
new file mode 100644
index 000000000..22bb4c4cb
--- /dev/null
+++ b/dwds/debug_extension_mv3/tool/update_dev_files.dart
@@ -0,0 +1,78 @@
+// Copyright (c) 2022, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:io';
+
+void main() async {
+  _updateManifestJson();
+}
+
+/// Adds the Googler extension key.
+Future<void> _updateManifestJson() async {
+  final manifestJson = File('compiled/manifest.json');
+  final extensionKeyTxt = File('extension_key.txt');
+  final extensionKey = await extensionKeyTxt.exists()
+      ? await extensionKeyTxt.readAsString()
+      : null;
+  _transformDevFile(manifestJson, (line) {
+    if (_matchesKey(line: line, key: 'name')) {
+      return [
+        line,
+        if (extensionKey != null)
+          _newKeyValue(
+            oldLine: line,
+            newKey: 'key',
+            newValue: extensionKey,
+          ),
+      ];
+    } else {
+      return [line];
+    }
+  });
+}
+
+Future<void> _transformDevFile(
+    File devFile, List<String> Function(String) transformLine) async {
+  final lines = devFile.readAsLinesSync();
+  final newLines = <String>[];
+  for (final line in lines) {
+    newLines.addAll(transformLine(line));
+  }
+  final content = newLines.joinWithNewLine();
+  return devFile.writeAsStringSync(content);
+}
+
+bool _matchesKey({required String line, required String key}) {
+  return line.trimLeft().startsWith('"$key":');
+}
+
+String _newKeyValue({
+  required String oldLine,
+  String? newKey,
+  String? newValue,
+}) {
+  final lineStart = oldLine.leftPadding();
+  final key = newKey != null ? '"$newKey": ' : '';
+  final value = newValue != null ? '"$newValue"' : '';
+  final lineEnd = oldLine.trim().endsWith(',') ? ',' : '';
+  return '$lineStart$key$value$lineEnd';
+}
+
+extension LeftPaddingExtension on String {
+  String leftPadding() {
+    String padding = '';
+    int idx = 0;
+    while (idx < length && this[idx] == ' ') {
+      padding += ' ';
+      idx++;
+    }
+    return padding;
+  }
+}
+
+extension JoinExtension on List<String> {
+  String joinWithNewLine() {
+    return '${join('\n')}\n';
+  }
+}
diff --git a/dwds/debug_extension_mv3/web/background.dart b/dwds/debug_extension_mv3/web/background.dart
new file mode 100644
index 000000000..b1478cba4
--- /dev/null
+++ b/dwds/debug_extension_mv3/web/background.dart
@@ -0,0 +1,19 @@
+// Copyright (c) 2022, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+@JS()
+library background;
+
+import 'package:js/js.dart';
+
+import 'chrome_api.dart';
+import 'web_api.dart';
+
+void main() {
+  console.log('Running Dart Debug Extension.');
+  // Detect clicks on the Dart Debug Extension icon.
+  chrome.action.onClicked.addListener(allowInterop((_) {
+    console.log('Detected click on the Dart Debug Extension icon.');
+  }));
+}
diff --git a/dwds/debug_extension_mv3/web/chrome_api.dart b/dwds/debug_extension_mv3/web/chrome_api.dart
new file mode 100644
index 000000000..9bc20b02e
--- /dev/null
+++ b/dwds/debug_extension_mv3/web/chrome_api.dart
@@ -0,0 +1,34 @@
+// Copyright (c) 2022, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:js/js.dart';
+
+@JS()
+external Chrome get chrome;
+
+@JS()
+@anonymous
+class Chrome {
+  external Action get action;
+}
+
+@JS()
+@anonymous
+class Action {
+  // https://developer.chrome.com/docs/extensions/reference/action/#event-onClicked
+  external OnClickedHandler get onClicked;
+}
+
+@JS()
+@anonymous
+class OnClickedHandler {
+  external void addListener(void Function(Tab tab) callback);
+}
+
+@JS()
+@anonymous
+class Tab {
+  external int get id;
+  external String get url;
+}
diff --git a/dwds/debug_extension_mv3/web/dart_dev.png b/dwds/debug_extension_mv3/web/dart_dev.png
new file mode 100644
index 000000000..8d0479209
Binary files /dev/null and b/dwds/debug_extension_mv3/web/dart_dev.png differ
diff --git a/dwds/debug_extension_mv3/web/manifest.json b/dwds/debug_extension_mv3/web/manifest.json
new file mode 100644
index 000000000..4434a260a
--- /dev/null
+++ b/dwds/debug_extension_mv3/web/manifest.json
@@ -0,0 +1,11 @@
+{
+    "name": "[MV3] Dart Debug Extension",
+    "version": "1.0",
+    "manifest_version": 3,
+    "action": {
+        "default_icon": "dart_dev.png"
+    },
+    "background": {
+        "service_worker": "background.dart.js"
+    }
+}
diff --git a/dwds/debug_extension_mv3/web/web_api.dart b/dwds/debug_extension_mv3/web/web_api.dart
new file mode 100644
index 000000000..8b927b405
--- /dev/null
+++ b/dwds/debug_extension_mv3/web/web_api.dart
@@ -0,0 +1,15 @@
+// Copyright (c) 2022, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:js/js.dart';
+
+@JS()
+external Console get console;
+
+@JS()
+@anonymous
+class Console {
+  external void log(String header,
+      [String style1, String style2, String style3]);
+}