feat: support Chrome extensions debugging

README.md

@@ -511,6 +511,12 @@ If you run into any issues, checkout our [troubleshooting guide](./docs/troubles
   - [`list_console_messages`](docs/tool-reference.md#list_console_messages)
   - [`take_screenshot`](docs/tool-reference.md#take_screenshot)
   - [`take_snapshot`](docs/tool-reference.md#take_snapshot)
+- **Extensions** (5 tools)
+  - [`install_extension`](docs/tool-reference.md#install_extension)
+  - [`list_extensions`](docs/tool-reference.md#list_extensions)
+  - [`reload_extension`](docs/tool-reference.md#reload_extension)
+  - [`trigger_extension_action`](docs/tool-reference.md#trigger_extension_action)
+  - [`uninstall_extension`](docs/tool-reference.md#uninstall_extension)
 - **Memory** (1 tools)
   - [`take_memory_snapshot`](docs/tool-reference.md#take_memory_snapshot)
 
@@ -612,6 +618,11 @@ The Chrome DevTools MCP server supports the following configuration option:
   - **Type:** boolean
   - **Default:** `true`
 
+- **`--categoryExtensions`/ `--category-extensions`**
+  Set to true to include tools related to extensions. Note: This feature is currently only supported with a pipe connection. autoConnect, browserUrl, and wsEndpoint are not supported with this feature until 149 will be released.
+  - **Type:** boolean
+  - **Default:** `false`
+
 - **`--performanceCrux`/ `--performance-crux`**
   Set to false to disable sending URLs from performance traces to CrUX API to get field performance data.
   - **Type:** boolean

docs/tool-reference.md

@@ -36,6 +36,12 @@
   - [`list_console_messages`](#list_console_messages)
   - [`take_screenshot`](#take_screenshot)
   - [`take_snapshot`](#take_snapshot)
+- **[Extensions](#extensions)** (5 tools)
+  - [`install_extension`](#install_extension)
+  - [`list_extensions`](#list_extensions)
+  - [`reload_extension`](#reload_extension)
+  - [`trigger_extension_action`](#trigger_extension_action)
+  - [`uninstall_extension`](#uninstall_extension)
 - **[Memory](#memory)** (1 tools)
   - [`take_memory_snapshot`](#take_memory_snapshot)
 
@@ -390,6 +396,58 @@ in the DevTools Elements panel (if any).
 
 ---
 
+## Extensions
+
+> NOTE: Extensions are not active by default. Use the '--category-extensions' flag
+
+### `install_extension`
+
+**Description:** Installs a Chrome extension from the given path.
+
+**Parameters:**
+
+- **path** (string) **(required)**: Absolute path to the unpacked extension folder.
+
+---
+
+### `list_extensions`
+
+**Description:** Lists all the Chrome extensions installed in the browser. This includes their name, ID, version, and enabled status.
+
+**Parameters:** None
+
+---
+
+### `reload_extension`
+
+**Description:** Reloads an unpacked Chrome extension by its ID.
+
+**Parameters:**
+
+- **id** (string) **(required)**: ID of the extension to reload.
+
+---
+
+### `trigger_extension_action`
+
+**Description:** Triggers the default action of an extension by its ID.
+
+**Parameters:**
+
+- **id** (string) **(required)**: ID of the extension to trigger the action for.
+
+---
+
+### `uninstall_extension`
+
+**Description:** Uninstalls a Chrome extension by its ID.
+
+**Parameters:**
+
+- **id** (string) **(required)**: ID of the extension to uninstall.
+
+---
+
 ## Memory
 
 ### `take_memory_snapshot`

scripts/generate-docs.ts

@@ -13,7 +13,11 @@ import {get_encoding} from 'tiktoken';
 
 import {cliOptions} from '../build/src/bin/chrome-devtools-mcp-cli-options.js';
 import type {ParsedArguments} from '../build/src/bin/chrome-devtools-mcp-cli-options.js';
-import {ToolCategory, labels} from '../build/src/tools/categories.js';
+import {
+  ToolCategory,
+  OFF_BY_DEFAULT_CATEGORIES,
+  labels,
+} from '../build/src/tools/categories.js';
 import {createTools} from '../build/src/tools/tools.js';
 
 const OUTPUT_PATH = './docs/tool-reference.md';
@@ -351,6 +355,12 @@ async function generateReference(
 
     markdown += `## ${categoryName}\n\n`;
 
+    if (OFF_BY_DEFAULT_CATEGORIES.includes(category)) {
+      const flagName = `--category-${category}`;
+
+      markdown += `> NOTE: ${categoryName} are not active by default. Use the '${flagName}' flag\n\n`;
+    }
+
     // Sort tools within category
     categoryTools.sort((a: Tool, b: Tool) => a.name.localeCompare(b.name));
 

skills/chrome-devtools/SKILL.md

@@ -5,8 +5,7 @@ description: Uses Chrome DevTools via MCP for efficient debugging, troubleshooti
 
 ## Core Concepts
 
-**Browser lifecycle**: Browser starts automatically on first tool call using a persistent Chrome profile. Configure via CLI args in the MCP server configuration: `npx chrome-devtools-mcp@latest --help`.
-
+**Browser lifecycle**: Browser starts automatically on first tool call using a persistent Chrome profile. Configure via CLI args in the MCP server configuration: `npx chrome-devtools-mcp@latest --help`. To enable extensions, use `--categoryExtensions`.
 **Page selection**: Tools operate on the currently selected page. Use `list_pages` to see available pages, then `select_page` to switch context.
 
 **Element interaction**: Use `take_snapshot` to get page structure with element `uid`s. Each element has a unique `uid` for interaction. If an element isn't found, take a fresh snapshot - the element may have been removed or the page changed.
@@ -36,6 +35,14 @@ description: Uses Chrome DevTools via MCP for efficient debugging, troubleshooti
 
 You can send multiple tool calls in parallel, but maintain correct order: navigate → wait → snapshot → interact.
 
+### Testing an extension
+
+1. **Install**: Use `install_extension` with the path to the unpacked extension.
+2. **Identify**: Get the extension ID from the response or by calling `list_extensions`.
+3. **Trigger Action**: Use `trigger_extension_action` to open the popup or side panel if applicable.
+4. **Verify Service Worker**: Use `evaluate_script` with `serviceWorkerId` to check extension state or trigger background actions.
+5. **Verify Page Behavior**: Navigate to a page where the extension operates and use `take_snapshot` to check if content scripts injected elements or modified the page correctly.
+
 ## Troubleshooting
 
 If `chrome-devtools-mcp` is insufficient, guide users to use Chrome DevTools UI:

skills/troubleshooting/SKILL.md

@@ -47,6 +47,13 @@ If the server starts successfully but only a limited subset of tools (like `list
 
 All tools in `chrome-devtools-mcp` are annotated with `readOnlyHint: true` (for safe, non-modifying tools) or `readOnlyHint: false` (for tools that modify browser state, like `emulate`, `click`, `navigate_page`). To access the full suite of tools, the user must disable read-only mode in their MCP client (e.g., by exiting "Plan Mode" in Gemini CLI or adjusting their client's tool safety settings).
 
+#### Symptom: Extension tools are missing or extensions fail to load
+
+If the tools related to extensions (like `install_extension`) are not available, or if the extensions you load are not functioning:
+
+1. **Check for the `--categoryExtensions` flag**: Ensure this flag is passed in the MCP server configuration to enable the extension category tools.
+2. **Make sure the MCP server in configured to launch Chrome instead of connecting to an instance**: Chrome before 149 is not able to load extensions when connecting to an existing instance (`--auto-connect`, `--browserUrl`).
+
 #### Other Common Errors
 
 Identify other error messages from the failed tool call or the MCP initialization logs:

src/bin/chrome-devtools-mcp-cli-options.ts

@@ -12,7 +12,7 @@ export const cliOptions = {
     type: 'boolean',
     description:
       'If specified, automatically connects to a browser (Chrome 144+) running locally from the user data directory identified by the channel param (default channel is stable). Requires the remote debugging server to be started in the Chrome instance via chrome://inspect/#remote-debugging.',
-    conflicts: ['isolated', 'executablePath', 'categoryExtensions'],
+    conflicts: ['isolated', 'executablePath'],
     default: false,
     coerce: (value: boolean | undefined) => {
       if (!value) {
@@ -26,7 +26,7 @@ export const cliOptions = {
     description:
       'Connect to a running, debuggable Chrome instance (e.g. `http://127.0.0.1:9222`). For more details see: https://github.com/ChromeDevTools/chrome-devtools-mcp#connecting-to-a-running-chrome-instance.',
     alias: 'u',
-    conflicts: ['wsEndpoint', 'categoryExtensions'],
+    conflicts: ['wsEndpoint'],
     coerce: (url: string | undefined) => {
       if (!url) {
         return;
@@ -44,7 +44,7 @@ export const cliOptions = {
     description:
       'WebSocket endpoint to connect to a running Chrome instance (e.g., ws://127.0.0.1:9222/devtools/browser/<id>). Alternative to --browserUrl.',
     alias: 'w',
-    conflicts: ['browserUrl', 'categoryExtensions'],
+    conflicts: ['browserUrl'],
     coerce: (url: string | undefined) => {
       if (!url) {
         return;
@@ -222,10 +222,10 @@ export const cliOptions = {
   },
   categoryExtensions: {
     type: 'boolean',
-    hidden: true,
-    conflicts: ['browserUrl', 'autoConnect', 'wsEndpoint'],
+    hidden: false,
+    default: false,
     describe:
-      'Set to true to include tools related to extensions. Note: This feature is only supported with a pipe connection. autoConnect is not supported.',
+      'Set to true to include tools related to extensions. Note: This feature is currently only supported with a pipe connection. autoConnect, browserUrl, and wsEndpoint are not supported with this feature until 149 will be released.',
   },
   categoryInPageTools: {
     type: 'boolean',

src/index.ts

@@ -136,7 +136,7 @@ export async function createMcpServer(
     }
     if (
       tool.annotations.category === ToolCategory.EXTENSIONS &&
-      !serverArgs.categoryExtensions
+      serverArgs.categoryExtensions === false
     ) {
       return;
     }

src/tools/categories.ts

@@ -27,3 +27,5 @@ export const labels = {
   [ToolCategory.IN_PAGE]: 'In-page tools',
   [ToolCategory.MEMORY]: 'Memory',
 };
+
+export const OFF_BY_DEFAULT_CATEGORIES = [ToolCategory.EXTENSIONS];

src/tools/console.ts

@@ -37,58 +37,61 @@ const FILTERABLE_MESSAGE_TYPES: [
   'issue',
 ];
 
-export const listConsoleMessages = definePageTool({
-  name: 'list_console_messages',
-  description:
-    'List all console messages for the currently selected page since the last navigation.',
-  annotations: {
-    category: ToolCategory.DEBUGGING,
-    readOnlyHint: true,
-  },
-  schema: {
-    pageSize: zod
-      .number()
-      .int()
-      .positive()
-      .optional()
-      .describe(
-        'Maximum number of messages to return. When omitted, returns all messages.',
-      ),
-    pageIdx: zod
-      .number()
-      .int()
-      .min(0)
-      .optional()
-      .describe(
-        'Page number to return (0-based). When omitted, returns the first page.',
-      ),
-    types: zod
-      .array(zod.enum(FILTERABLE_MESSAGE_TYPES))
-      .optional()
-      .describe(
-        'Filter messages to only return messages of the specified resource types. When omitted or empty, returns all messages.',
-      ),
-    includePreservedMessages: zod
-      .boolean()
-      .default(false)
-      .optional()
-      .describe(
-        'Set to true to return the preserved messages over the last 3 navigations.',
-      ),
-  },
-  handler: async (request, response) => {
-    response.setIncludeConsoleData(true, {
-      pageSize: request.params.pageSize,
-      pageIdx: request.params.pageIdx,
-      types: request.params.types,
-      includePreservedMessages: request.params.includePreservedMessages,
-    });
-  },
+const LIST_CONSOLE_MESSAGES_TOOL_NAME = 'list_console_messages';
+
+export const listConsoleMessages = definePageTool(cliArgs => {
+  return {
+    name: LIST_CONSOLE_MESSAGES_TOOL_NAME,
+    description: `List all console messages for the currently selected page since the last navigation.${cliArgs?.categoryExtensions ? ' This includes console messages originating from extensions content scripts.' : ''}`,
+    annotations: {
+      category: ToolCategory.DEBUGGING,
+      readOnlyHint: true,
+    },
+    schema: {
+      pageSize: zod
+        .number()
+        .int()
+        .positive()
+        .optional()
+        .describe(
+          'Maximum number of messages to return. When omitted, returns all messages.',
+        ),
+      pageIdx: zod
+        .number()
+        .int()
+        .min(0)
+        .optional()
+        .describe(
+          'Page number to return (0-based). When omitted, returns the first page.',
+        ),
+      types: zod
+        .array(zod.enum(FILTERABLE_MESSAGE_TYPES))
+        .optional()
+        .describe(
+          'Filter messages to only return messages of the specified resource types. When omitted or empty, returns all messages.',
+        ),
+      includePreservedMessages: zod
+        .boolean()
+        .default(false)
+        .optional()
+        .describe(
+          'Set to true to return the preserved messages over the last 3 navigations.',
+        ),
+    },
+    handler: async (request, response) => {
+      response.setIncludeConsoleData(true, {
+        pageSize: request.params.pageSize,
+        pageIdx: request.params.pageIdx,
+        types: request.params.types,
+        includePreservedMessages: request.params.includePreservedMessages,
+      });
+    },
+  };
 });
 
 export const getConsoleMessage = definePageTool({
   name: 'get_console_message',
-  description: `Gets a console message by its ID. You can get all messages by calling ${listConsoleMessages.name}.`,
+  description: `Gets a console message by its ID. You can get all messages by calling ${LIST_CONSOLE_MESSAGES_TOOL_NAME}.`,
   annotations: {
     category: ToolCategory.DEBUGGING,
     readOnlyHint: true,

src/tools/extensions.ts

@@ -9,15 +9,12 @@ import {zod} from '../third_party/index.js';
 import {ToolCategory} from './categories.js';
 import {defineTool} from './ToolDefinition.js';
 
-const EXTENSIONS_CONDITION = 'experimentalExtensionSupport';
-
 export const installExtension = defineTool({
   name: 'install_extension',
   description: 'Installs a Chrome extension from the given path.',
   annotations: {
     category: ToolCategory.EXTENSIONS,
     readOnlyHint: false,
-    conditions: [EXTENSIONS_CONDITION],
   },
   schema: {
     path: zod
@@ -37,7 +34,6 @@ export const uninstallExtension = defineTool({
   annotations: {
     category: ToolCategory.EXTENSIONS,
     readOnlyHint: false,
-    conditions: [EXTENSIONS_CONDITION],
   },
   schema: {
     id: zod.string().describe('ID of the extension to uninstall.'),
@@ -52,11 +48,10 @@ export const uninstallExtension = defineTool({
 export const listExtensions = defineTool({
   name: 'list_extensions',
   description:
-    'Lists all extensions via this server, including their name, ID, version, and enabled status.',
+    'Lists all the Chrome extensions installed in the browser. This includes their name, ID, version, and enabled status.',
   annotations: {
     category: ToolCategory.EXTENSIONS,
     readOnlyHint: true,
-    conditions: [EXTENSIONS_CONDITION],
   },
   schema: {},
   handler: async (_request, response, _context) => {
@@ -70,7 +65,6 @@ export const reloadExtension = defineTool({
   annotations: {
     category: ToolCategory.EXTENSIONS,
     readOnlyHint: false,
-    conditions: [EXTENSIONS_CONDITION],
   },
   schema: {
     id: zod.string().describe('ID of the extension to reload.'),
@@ -88,18 +82,17 @@ export const reloadExtension = defineTool({
 
 export const triggerExtensionAction = defineTool({
   name: 'trigger_extension_action',
-  description: 'Triggers an action in a Chrome extension.',
+  description: 'Triggers the default action of an extension by its ID.',
   annotations: {
     category: ToolCategory.EXTENSIONS,
     readOnlyHint: false,
-    conditions: [EXTENSIONS_CONDITION],
   },
   schema: {
-    id: zod.string().describe('ID of the extension.'),
+    id: zod.string().describe('ID of the extension to trigger the action for.'),
   },
   handler: async (request, response, context) => {
     const {id} = request.params;
     await context.triggerExtensionAction(id);
-    response.appendResponseLine(`Extension action triggered. Id: ${id}`);
+    response.appendResponseLine(`Extension action triggered for ID ${id}`);
   },
 });