feat: add storage-isolated browser contexts (#991)

## Summary

Adds storage-isolated browser contexts via an optional `isolatedContext`
parameter on the `new_page` tool, following the simplified design
proposed by @OrKoN in #926.

Pages created with the same `isolatedContext` name share cookies,
localStorage, and storage. Pages in different isolated contexts (or the
default context) are fully isolated — ideal for testing multi-user
real-time features like chat, notifications, or collaborative editing.

## Changes

### `new_page` tool
- New optional `isolatedContext: string` parameter
- If specified, creates/reuses a named `BrowserContext` and opens a page
in it
- If omitted, uses the default browser context (existing behavior
unchanged)

### `McpContext`
- `#isolatedContexts` Map: LLM-provided names → Puppeteer
`BrowserContext` instances
- `#pageToIsolatedContextName` WeakMap: GC-safe page → context name
reverse lookup
- Auto-discovery: externally created browser contexts get
`isolated-context-1`, `isolated-context-2`, etc.
- `getIsolatedContextName(page)`: returns the isolated context name for
a page (used by response formatting)
- `page.browserContext()` used for context membership detection (no
custom target event forwarding needed)
- No context cleanup in `dispose()` or `closePage()` — either the entire
browser is closed or we disconnect without destroying state

### `McpResponse`
- Page list includes `isolatedContext=${name}` labels (both text and
structured JSON output)

### `ToolDefinition`
- `Context` interface extended with `getIsolatedContextName(page)`
method

## What's NOT included (by design)
- **No `TargetEventEmitter`**: Puppeteer forwards target events from
`BrowserContext` → `Browser` internally
- **No context cleanup**: Browser contexts are not closed on `dispose()`
or page close, per maintainer guidance
- **No `about:blank` cleanup**: Default context and isolated contexts
coexist side-by-side

## Example

```
> new_page url="https://app.example.com/chat" isolatedContext="userA"
> new_page url="https://app.example.com/chat" isolatedContext="userB"
> list_pages

Page 1: [app.example.com/chat] isolatedContext=userA
Page 2: [app.example.com/chat] isolatedContext=userB [selected]
```

Pages in different isolated contexts have fully independent cookies,
localStorage, IndexedDB, and WebSocket connections.

## Tests

- 6 new tests covering `isolatedContext` feature in
`tests/tools/pages.test.ts`
- All existing tests pass (333+)
- Zero type errors, lint clean

Closes #926

---------

Co-authored-by: Alex Rudenko <alexrudenko@chromium.org>

Author: RobertWsp

docs/tool-reference.md

@@ -1,6 +1,6 @@
 <!-- AUTO GENERATED DO NOT EDIT - run 'npm run docs' to update-->
 
-# Chrome DevTools MCP Tool Reference (~6661 cl100k_base tokens)
+# Chrome DevTools MCP Tool Reference (~6719 cl100k_base tokens)
 
 - **[Input automation](#input-automation)** (8 tools)
   - [`click`](#click)
@@ -172,6 +172,7 @@
 
 - **url** (string) **(required)**: URL to load in a new page.
 - **background** (boolean) _(optional)_: Whether to open the page in the background without bringing it to the front. Default is false (foreground).
+- **isolatedContext** (string) _(optional)_: If specified, the page is created in an isolated browser context with the given name. Pages in the same browser context share cookies and storage. Pages in different browser contexts are fully isolated.
 - **timeout** (integer) _(optional)_: Maximum wait time in milliseconds. If set to 0, the default timeout will be used.
 
 ---

scripts/eval_scenarios/isolated_context_test.ts

@@ -0,0 +1,31 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import assert from 'node:assert';
+
+import type {TestScenario} from '../eval_gemini.ts';
+
+export const scenario: TestScenario = {
+  prompt:
+    'Create a new page <TEST_URL> in an isolated context called contextB. Take a screenshot there.',
+  maxTurns: 3,
+  htmlRoute: {
+    path: '/test.html',
+    htmlContent: `
+      <h1>test</h1>
+    `,
+  },
+  expectations: calls => {
+    console.log(JSON.stringify(calls, null, 2));
+    assert.strictEqual(calls.length, 2);
+    assert.ok(calls[0].name === 'new_page', 'First call should be navigation');
+    assert.deepStrictEqual(calls[0].args.isolatedContext, 'contextB');
+    assert.ok(
+      calls[1].name === 'take_screenshot',
+      'Second call should be a screenshot',
+    );
+  },
+};

src/McpContext.ts

@@ -19,6 +19,7 @@ import {NetworkCollector, ConsoleCollector} from './PageCollector.js';
 import type {DevTools} from './third_party/index.js';
 import type {
   Browser,
+  BrowserContext,
   ConsoleMessage,
   Debugger,
   Dialog,
@@ -119,11 +120,17 @@ export class McpContext implements Context {
   browser: Browser;
   logger: Debugger;
 
-  // The most recent page state.
+  // Maps LLM-provided isolatedContext name → Puppeteer BrowserContext.
+  #isolatedContexts = new Map<string, BrowserContext>();
+  // Reverse lookup: Page → isolatedContext name (for snapshot labeling).
+  // WeakMap so closed pages are garbage-collected automatically.
+  #pageToIsolatedContextName = new WeakMap<Page, string>();
+  // Auto-generated name counter for when no name is provided.
+  #nextIsolatedContextId = 1;
+
   #pages: Page[] = [];
   #pageToDevToolsPage = new Map<Page, Page>();
   #selectedPage?: Page;
-  // The most recent snapshot.
   #textSnapshot: TextSnapshot | null = null;
   #networkCollector: NetworkCollector;
   #consoleCollector: ConsoleCollector;
@@ -187,6 +194,10 @@ export class McpContext implements Context {
     this.#networkCollector.dispose();
     this.#consoleCollector.dispose();
     this.#devtoolsUniverseManager.dispose();
+    // Isolated contexts are intentionally not closed here.
+    // Either the entire browser will be closed or we disconnect
+    // without destroying browser state.
+    this.#isolatedContexts.clear();
   }
 
   static async from(
@@ -269,8 +280,22 @@ export class McpContext implements Context {
     return this.#consoleCollector.getById(this.getSelectedPage(), id);
   }
 
-  async newPage(background?: boolean): Promise<Page> {
-    const page = await this.browser.newPage({background});
+  async newPage(
+    background?: boolean,
+    isolatedContextName?: string,
+  ): Promise<Page> {
+    let page: Page;
+    if (isolatedContextName !== undefined) {
+      let ctx = this.#isolatedContexts.get(isolatedContextName);
+      if (!ctx) {
+        ctx = await this.browser.createBrowserContext();
+        this.#isolatedContexts.set(isolatedContextName, ctx);
+      }
+      page = await ctx.newPage();
+      this.#pageToIsolatedContextName.set(page, isolatedContextName);
+    } else {
+      page = await this.browser.newPage({background});
+    }
     await this.createPagesSnapshot();
     this.selectPage(page);
     this.#networkCollector.addPage(page);
@@ -283,6 +308,7 @@ export class McpContext implements Context {
     }
     const page = this.getPageById(pageId);
     await page.close({runBeforeUnload: false});
+    this.#pageToIsolatedContextName.delete(page);
   }
 
   getNetworkRequestById(reqid: number): HTTPRequest {
@@ -558,13 +584,8 @@ export class McpContext implements Context {
     }
   }
 
-  /**
-   * Creates a snapshot of the pages.
-   */
   async createPagesSnapshot(): Promise<Page[]> {
-    const allPages = await this.browser.pages(
-      this.#options.experimentalIncludeAllPages,
-    );
+    const allPages = await this.#getAllPages();
 
     for (const page of allPages) {
       if (!this.#pageIdMap.has(page)) {
@@ -573,8 +594,6 @@ export class McpContext implements Context {
     }
 
     this.#pages = allPages.filter(page => {
-      // If we allow debugging DevTools windows, return all pages.
-      // If we are in regular mode, the user should only see non-DevTools page.
       return (
         this.#options.experimentalDevToolsDebugging ||
         !page.url().startsWith('devtools://')
@@ -593,11 +612,44 @@ export class McpContext implements Context {
     return this.#pages;
   }
 
-  async detectOpenDevToolsWindows() {
-    this.logger('Detecting open DevTools windows');
-    const pages = await this.browser.pages(
+  async #getAllPages(): Promise<Page[]> {
+    const defaultCtx = this.browser.defaultBrowserContext();
+    const allPages = await this.browser.pages(
       this.#options.experimentalIncludeAllPages,
     );
+
+    // Build a reverse lookup from BrowserContext instance → name.
+    const contextToName = new Map<BrowserContext, string>();
+    for (const [name, ctx] of this.#isolatedContexts) {
+      contextToName.set(ctx, name);
+    }
+
+    // Auto-discover BrowserContexts not in our mapping (e.g., externally
+    // created incognito contexts) and assign generated names.
+    const knownContexts = new Set(this.#isolatedContexts.values());
+    for (const ctx of this.browser.browserContexts()) {
+      if (ctx !== defaultCtx && !ctx.closed && !knownContexts.has(ctx)) {
+        const name = `isolated-context-${this.#nextIsolatedContextId++}`;
+        this.#isolatedContexts.set(name, ctx);
+        contextToName.set(ctx, name);
+      }
+    }
+
+    // Use page.browserContext() to determine each page's context membership.
+    for (const page of allPages) {
+      const ctx = page.browserContext();
+      const name = contextToName.get(ctx);
+      if (name) {
+        this.#pageToIsolatedContextName.set(page, name);
+      }
+    }
+
+    return allPages;
+  }
+
+  async detectOpenDevToolsWindows() {
+    this.logger('Detecting open DevTools windows');
+    const pages = await this.#getAllPages();
     this.#pageToDevToolsPage = new Map<Page, Page>();
     for (const devToolsPage of pages) {
       if (devToolsPage.url().startsWith('devtools://')) {
@@ -629,6 +681,10 @@ export class McpContext implements Context {
     return this.#pages;
   }
 
+  getIsolatedContextName(page: Page): string | undefined {
+    return this.#pageToIsolatedContextName.get(page);
+  }
+
   getDevToolsPage(page: Page): Page | undefined {
     return this.#pageToDevToolsPage.get(page);
   }
@@ -857,7 +913,8 @@ export class McpContext implements Context {
         },
       } as ListenerMap;
     });
-    await this.#networkCollector.init(await this.browser.pages());
+    const pages = await this.#getAllPages();
+    await this.#networkCollector.init(pages);
   }
 
   async installExtension(extensionPath: string): Promise<string> {

src/McpResponse.ts

@@ -504,17 +504,31 @@ Call ${handleDialog.name} to handle it before continuing.`);
     if (this.#includePages) {
       const parts = [`## Pages`];
       for (const page of context.getPages()) {
+        const isolatedContextName = context.getIsolatedContextName(page);
+        const contextLabel = isolatedContextName
+          ? ` isolatedContext=${isolatedContextName}`
+          : '';
         parts.push(
-          `${context.getPageId(page)}: ${page.url()}${context.isPageSelected(page) ? ' [selected]' : ''}`,
+          `${context.getPageId(page)}: ${page.url()}${context.isPageSelected(page) ? ' [selected]' : ''}${contextLabel}`,
         );
       }
       response.push(...parts);
       structuredContent.pages = context.getPages().map(page => {
-        return {
+        const isolatedContextName = context.getIsolatedContextName(page);
+        const entry: {
+          id: number | undefined;
+          url: string;
+          selected: boolean;
+          isolatedContext?: string;
+        } = {
           id: context.getPageId(page),
           url: page.url(),
           selected: context.isPageSelected(page),
         };
+        if (isolatedContextName) {
+          entry.isolatedContext = isolatedContextName;
+        }
+        return entry;
       });
     }
 

src/tools/ToolDefinition.ts

@@ -112,9 +112,10 @@ export type Context = Readonly<{
   getPageById(pageId: number): Page;
   getPageId(page: Page): number | undefined;
   isPageSelected(page: Page): boolean;
-  newPage(background?: boolean): Promise<Page>;
+  newPage(background?: boolean, isolatedContextName?: string): Promise<Page>;
   closePage(pageId: number): Promise<void>;
   selectPage(page: Page): void;
+  getIsolatedContextName(page: Page): string | undefined;
   getElementByUid(uid: string): Promise<ElementHandle<Element>>;
   getAXNodeByUid(uid: string): TextSnapshotNode | undefined;
   emulate(options: {

src/tools/pages.ts

@@ -93,10 +93,21 @@ export const newPage = defineTool({
       .describe(
         'Whether to open the page in the background without bringing it to the front. Default is false (foreground).',
       ),
+    isolatedContext: zod
+      .string()
+      .optional()
+      .describe(
+        'If specified, the page is created in an isolated browser context with the given name. ' +
+          'Pages in the same browser context share cookies and storage. ' +
+          'Pages in different browser contexts are fully isolated.',
+      ),
     ...timeoutSchema,
   },
   handler: async (request, response, context) => {
-    const page = await context.newPage(request.params.background);
+    const page = await context.newPage(
+      request.params.background,
+      request.params.isolatedContext,
+    );
 
     await context.waitForEventsAfterAction(
       async () => {

tests/tools/pages.test.ts

@@ -73,6 +73,109 @@ describe('pages', () => {
       });
     });
   });
+  describe('new_page with isolatedContext', () => {
+    it('creates a page in an isolated context', async () => {
+      await withMcpContext(async (response, context) => {
+        await newPage.handler(
+          {params: {url: 'about:blank', isolatedContext: 'session-a'}},
+          response,
+          context,
+        );
+        const page = context.getSelectedPage();
+        assert.strictEqual(context.getIsolatedContextName(page), 'session-a');
+        assert.ok(response.includePages);
+      });
+    });
+
+    it('reuses the same context for the same isolatedContext name', async () => {
+      await withMcpContext(async (response, context) => {
+        await newPage.handler(
+          {params: {url: 'about:blank', isolatedContext: 'session-a'}},
+          response,
+          context,
+        );
+        const page1 = context.getSelectedPage();
+        await newPage.handler(
+          {params: {url: 'about:blank', isolatedContext: 'session-a'}},
+          response,
+          context,
+        );
+        const page2 = context.getSelectedPage();
+        assert.notStrictEqual(page1, page2);
+        assert.strictEqual(context.getIsolatedContextName(page1), 'session-a');
+        assert.strictEqual(context.getIsolatedContextName(page2), 'session-a');
+        assert.strictEqual(page1.browserContext(), page2.browserContext());
+      });
+    });
+
+    it('creates separate contexts for different isolatedContext names', async () => {
+      await withMcpContext(async (response, context) => {
+        await newPage.handler(
+          {params: {url: 'about:blank', isolatedContext: 'session-a'}},
+          response,
+          context,
+        );
+        const pageA = context.getSelectedPage();
+        await newPage.handler(
+          {params: {url: 'about:blank', isolatedContext: 'session-b'}},
+          response,
+          context,
+        );
+        const pageB = context.getSelectedPage();
+        assert.strictEqual(context.getIsolatedContextName(pageA), 'session-a');
+        assert.strictEqual(context.getIsolatedContextName(pageB), 'session-b');
+        assert.notStrictEqual(pageA.browserContext(), pageB.browserContext());
+      });
+    });
+
+    it('includes isolatedContext in page listing', async () => {
+      await withMcpContext(async (response, context) => {
+        await newPage.handler(
+          {params: {url: 'about:blank', isolatedContext: 'session-a'}},
+          response,
+          context,
+        );
+        const result = await response.handle('new_page', context);
+        const pages = (
+          result.structuredContent as {pages: Array<{isolatedContext?: string}>}
+        ).pages;
+        const isolatedPage = pages.find(p => p.isolatedContext === 'session-a');
+        assert.ok(isolatedPage);
+      });
+    });
+
+    it('does not set isolatedContext for pages in the default context', async () => {
+      await withMcpContext(async (response, context) => {
+        const page = context.getSelectedPage();
+        assert.strictEqual(context.getIsolatedContextName(page), undefined);
+        await newPage.handler(
+          {params: {url: 'about:blank'}},
+          response,
+          context,
+        );
+        assert.strictEqual(
+          context.getIsolatedContextName(context.getSelectedPage()),
+          undefined,
+        );
+      });
+    });
+
+    it('closes an isolated page without errors', async () => {
+      await withMcpContext(async (response, context) => {
+        await newPage.handler(
+          {params: {url: 'about:blank', isolatedContext: 'session-a'}},
+          response,
+          context,
+        );
+        const page = context.getSelectedPage();
+        const pageId = context.getPageId(page)!;
+        assert.ok(!page.isClosed());
+        await closePage.handler({params: {pageId}}, response, context);
+        assert.ok(page.isClosed());
+      });
+    });
+  });
+
   describe('close_page', () => {
     it('closes a page', async () => {
       await withMcpContext(async (response, context) => {