chore: implement list_extensions tool for local unpacked extensions

src/McpContext.ts

@@ -35,6 +35,10 @@ import {takeSnapshot} from './tools/snapshot.js';
 import {CLOSE_PAGE_ERROR} from './tools/ToolDefinition.js';
 import type {Context, DevToolsData} from './tools/ToolDefinition.js';
 import type {TraceResult} from './trace-processing/parse.js';
+import {
+  ExtensionRegistry,
+  type InstalledExtension,
+} from './utils/ExtensionRegistry.js';
 import {WaitForHelper} from './WaitForHelper.js';
 
 export interface TextSnapshotNode extends SerializedAXNode {
@@ -112,6 +116,7 @@ export class McpContext implements Context {
   #networkCollector: NetworkCollector;
   #consoleCollector: ConsoleCollector;
   #devtoolsUniverseManager: UniverseManager;
+  #extensionRegistry = new ExtensionRegistry();
 
   #isRunningTrace = false;
   #networkConditionsMap = new WeakMap<Page, string>();
@@ -753,11 +758,18 @@ export class McpContext implements Context {
     await this.#networkCollector.init(await this.browser.pages());
   }
 
-  async installExtension(path: string): Promise<string> {
-    return this.browser.installExtension(path);
+  async installExtension(extensionPath: string): Promise<string> {
+    const id = await this.browser.installExtension(extensionPath);
+    await this.#extensionRegistry.registerExtension(id, extensionPath);
+    return id;
   }
 
   async uninstallExtension(id: string): Promise<void> {
-    return this.browser.uninstallExtension(id);
+    await this.browser.uninstallExtension(id);
+    this.#extensionRegistry.remove(id);
+  }
+
+  listExtensions(): InstalledExtension[] {
+    return this.#extensionRegistry.list();
   }
 }

src/McpResponse.ts

@@ -25,6 +25,7 @@ import type {
 } from './tools/ToolDefinition.js';
 import type {InsightName, TraceResult} from './trace-processing/parse.js';
 import {getInsightOutput, getTraceSummary} from './trace-processing/parse.js';
+import type {InstalledExtension} from './utils/ExtensionRegistry.js';
 import {paginate} from './utils/pagination.js';
 import type {PaginationOptions} from './utils/types.js';
 
@@ -60,6 +61,7 @@ export class McpResponse implements Response {
     types?: string[];
     includePreservedMessages?: boolean;
   };
+  #listExtensions?: boolean;
   #devToolsData?: DevToolsData;
   #tabId?: string;
 
@@ -81,6 +83,10 @@ export class McpResponse implements Response {
     };
   }
 
+  setListExtensions(): void {
+    this.#listExtensions = true;
+  }
+
   setIncludeNetworkRequests(
     value: boolean,
     options?: PaginationOptions & {
@@ -297,6 +303,11 @@ export class McpResponse implements Response {
       }
     }
 
+    let extensions: InstalledExtension[] | undefined;
+    if (this.#listExtensions) {
+      extensions = context.listExtensions();
+    }
+
     let consoleMessages: Array<ConsoleFormatter | IssueFormatter> | undefined;
     if (this.#consoleDataOptions?.include) {
       let messages = context.getConsoleData(
@@ -395,6 +406,7 @@ export class McpResponse implements Response {
       networkRequests,
       traceInsight: this.#attachedTraceInsight,
       traceSummary: this.#attachedTraceSummary,
+      extensions,
     });
   }
 
@@ -409,6 +421,7 @@ export class McpResponse implements Response {
       networkRequests?: NetworkFormatter[];
       traceSummary?: TraceResult;
       traceInsight?: TraceInsightData;
+      extensions?: InstalledExtension[];
     },
   ): {content: Array<TextContent | ImageContent>; structuredContent: object} {
     const response = [`# ${toolName} response`];
@@ -474,6 +487,7 @@ Call ${handleDialog.name} to handle it before continuing.`);
       consoleMessages?: object[];
       traceSummary?: string;
       traceInsights?: Array<{insightName: string; insightKey: string}>;
+      extensions?: object[];
     } = {};
 
     if (this.#tabId) {
@@ -531,6 +545,21 @@ Call ${handleDialog.name} to handle it before continuing.`);
         data.detailedConsoleMessage.toJSONDetailed();
     }
 
+    if (data.extensions) {
+      structuredContent.extensions = data.extensions;
+      response.push('## Extensions');
+      if (data.extensions.length === 0) {
+        response.push('No extensions installed.');
+      } else {
+        const extensionsMessage = data.extensions
+          .map(extension => {
+            return `id=${extension.id} "${extension.name}" v${extension.version} ${extension.isEnabled ? 'Enabled' : 'Disabled'}`;
+          })
+          .join('\n');
+        response.push(extensionsMessage);
+      }
+    }
+
     if (this.#networkRequestsOptions?.include) {
       let requests = context.getNetworkRequests(
         this.#networkRequestsOptions?.includePreservedRequests,

src/tools/ToolDefinition.ts

@@ -13,6 +13,7 @@ import type {
   Viewport,
 } from '../third_party/index.js';
 import type {InsightName, TraceResult} from '../trace-processing/parse.js';
+import type {InstalledExtension} from '../utils/ExtensionRegistry.js';
 import type {PaginationOptions} from '../utils/types.js';
 
 import type {ToolCategory} from './categories.js';
@@ -92,6 +93,7 @@ export interface Response {
     insightSetId: string,
     insightName: InsightName,
   ): void;
+  setListExtensions(): void;
 }
 
 /**
@@ -141,6 +143,7 @@ export type Context = Readonly<{
   resolveCdpElementId(cdpBackendNodeId: number): string | undefined;
   installExtension(path: string): Promise<string>;
   uninstallExtension(id: string): Promise<void>;
+  listExtensions(): InstalledExtension[];
 }>;
 
 export function defineTool<Schema extends zod.ZodRawShape>(

src/tools/extensions.ts

@@ -48,3 +48,18 @@ export const uninstallExtension = defineTool({
     response.appendResponseLine(`Extension uninstalled. Id: ${id}`);
   },
 });
+
+export const listExtensions = defineTool({
+  name: 'list_extensions',
+  description:
+    'Lists all installed extensions, including their name, ID, version, and enabled status.',
+  annotations: {
+    category: ToolCategory.EXTENSIONS,
+    readOnlyHint: true,
+    conditions: [EXTENSIONS_CONDITION],
+  },
+  schema: {},
+  handler: async (_request, response, _context) => {
+    response.setListExtensions();
+  },
+});

src/utils/ExtensionRegistry.ts

@@ -0,0 +1,53 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import fs from 'node:fs/promises';
+import path from 'node:path';
+
+export interface InstalledExtension {
+  id: string;
+  name: string;
+  version: string;
+  isEnabled: boolean;
+  path: string;
+}
+
+export class ExtensionRegistry {
+  #extensions = new Map<string, InstalledExtension>();
+
+  async registerExtension(
+    id: string,
+    extensionPath: string,
+  ): Promise<InstalledExtension> {
+    const manifestPath = path.join(extensionPath, 'manifest.json');
+    const manifestContent = await fs.readFile(manifestPath, 'utf-8');
+    const manifest = JSON.parse(manifestContent);
+    const name = manifest.name ?? 'Unknown';
+    const version = manifest.version ?? 'Unknown';
+
+    const extension = {
+      id,
+      name,
+      version,
+      isEnabled: true,
+      path: extensionPath,
+    };
+    this.#extensions.set(extension.id, extension);
+    return extension;
+  }
+
+  remove(id: string): void {
+    this.#extensions.delete(id);
+  }
+
+  list(): InstalledExtension[] {
+    return Array.from(this.#extensions.values());
+  }
+
+  getById(id: string): InstalledExtension | undefined {
+    return this.#extensions.get(id);
+  }
+}

tests/McpResponse.test.js.snapshot

@@ -480,3 +480,31 @@ exports[`McpResponse network request filtering > shows no requests when filter m
 ## Network requests
 No requests found.
 `;
+
+exports[`extensions > lists extensions 1`] = `
+# test response
+## Extensions
+id=id1 "Extension 1" v1.0 Enabled
+id=id2 "Extension 2" v2.0 Disabled
+`;
+
+exports[`extensions > lists extensions 2`] = `
+{
+  "extensions": [
+    {
+      "id": "id1",
+      "name": "Extension 1",
+      "version": "1.0",
+      "isEnabled": true,
+      "path": "/path/to/ext1"
+    },
+    {
+      "id": "id2",
+      "name": "Extension 2",
+      "version": "2.0",
+      "isEnabled": false,
+      "path": "/path/to/ext2"
+    }
+  ]
+}
+`;

tests/McpResponse.test.ts

@@ -713,3 +713,45 @@ describe('McpResponse network pagination', () => {
     });
   });
 });
+
+describe('extensions', () => {
+  it('lists extensions', async t => {
+    await withMcpContext(async (response, context) => {
+      response.setListExtensions();
+      // Empty state testing
+      const emptyResult = await response.handle('test', context);
+      const emptyText = getTextContent(emptyResult.content[0]);
+      assert.ok(
+        emptyText.includes('No extensions installed.'),
+        'Should show message for ampty extensions',
+      );
+
+      response.resetResponseLineForTesting();
+      // Testing with extensions
+      context.listExtensions = () => [
+        {
+          id: 'id1',
+          name: 'Extension 1',
+          version: '1.0',
+          isEnabled: true,
+          path: '/path/to/ext1',
+        },
+        {
+          id: 'id2',
+          name: 'Extension 2',
+          version: '2.0',
+          isEnabled: false,
+          path: '/path/to/ext2',
+        },
+      ];
+      response.setListExtensions();
+      const {content, structuredContent} = await response.handle(
+        'test',
+        context,
+      );
+
+      t.assert.snapshot?.(getTextContent(content[0]));
+      t.assert.snapshot?.(JSON.stringify(structuredContent, null, 2));
+    });
+  });
+});

tests/tools/extensions.test.ts

@@ -8,9 +8,12 @@ import assert from 'node:assert';
 import path from 'node:path';
 import {describe, it} from 'node:test';
 
+import sinon from 'sinon';
+
 import {
   installExtension,
   uninstallExtension,
+  listExtensions,
 } from '../../src/tools/extensions.js';
 import {withMcpContext} from '../utils.js';
 
@@ -71,4 +74,14 @@ describe('extension', () => {
       );
     });
   });
+  it('lists installed extensions', async () => {
+    await withMcpContext(async (response, context) => {
+      const setListExtensionsSpy = sinon.spy(response, 'setListExtensions');
+      await listExtensions.handler({params: {}}, response, context);
+      assert.ok(
+        setListExtensionsSpy.calledOnce,
+        'setListExtensions should be called',
+      );
+    });
+  });
 });