feat: adding network request overrides

README.md

@@ -15,8 +15,9 @@ A [CLI](docs/cli.md) is also provided for use without MCP.
 - **Get performance insights**: Uses [Chrome
   DevTools](https://github.com/ChromeDevTools/devtools-frontend) to record
   traces and extract actionable performance insights.
-- **Advanced browser debugging**: Analyze network requests, take screenshots and
-  check browser console messages (with source-mapped stack traces).
+- **Advanced browser debugging**: Analyze and override network requests, take
+  screenshots and check browser console messages (with source-mapped stack
+  traces).
 - **Reliable automation**. Uses
   [puppeteer](https://github.com/puppeteer/puppeteer) to automate actions in
   Chrome and automatically wait for action results.
@@ -512,9 +513,12 @@ If you run into any issues, checkout our [troubleshooting guide](./docs/troubles
   - [`performance_analyze_insight`](docs/tool-reference.md#performance_analyze_insight)
   - [`performance_start_trace`](docs/tool-reference.md#performance_start_trace)
   - [`performance_stop_trace`](docs/tool-reference.md#performance_stop_trace)
-- **Network** (2 tools)
+- **Network** (5 tools)
+  - [`add_network_override`](docs/tool-reference.md#add_network_override)
   - [`get_network_request`](docs/tool-reference.md#get_network_request)
+  - [`list_network_overrides`](docs/tool-reference.md#list_network_overrides)
   - [`list_network_requests`](docs/tool-reference.md#list_network_requests)
+  - [`remove_network_override`](docs/tool-reference.md#remove_network_override)
 - **Debugging** (8 tools)
   - [`evaluate_script`](docs/tool-reference.md#evaluate_script)
   - [`get_console_message`](docs/tool-reference.md#get_console_message)

docs/tool-reference.md

@@ -27,9 +27,12 @@
   - [`performance_analyze_insight`](#performance_analyze_insight)
   - [`performance_start_trace`](#performance_start_trace)
   - [`performance_stop_trace`](#performance_stop_trace)
-- **[Network](#network)** (2 tools)
+- **[Network](#network)** (5 tools)
+  - [`add_network_override`](#add_network_override)
   - [`get_network_request`](#get_network_request)
+  - [`list_network_overrides`](#list_network_overrides)
   - [`list_network_requests`](#list_network_requests)
+  - [`remove_network_override`](#remove_network_override)
 - **[Debugging](#debugging)** (8 tools)
   - [`evaluate_script`](#evaluate_script)
   - [`get_console_message`](#get_console_message)
@@ -319,6 +322,20 @@
 
 ## Network
 
+### `add_network_override`
+
+**Description:** Adds a page-scoped network override that redirects matching requests or fulfills them from a local file. Add the override before navigating or reloading the page.
+
+**Parameters:**
+
+- **urlPattern** (string) **(required)**: CDP URL pattern to match. Use '*' for any sequence, '?' for one character, and a backslash to escape a wildcard.
+- **contentType** (string) _(optional)_: Content-Type for a local-file response. When omitted, it is inferred from the file extension.
+- **redirectUrl** (string) _(optional)_: Absolute HTTP(S) URL to load instead. Exactly one of redirectUrl or responseFilePath is required.
+- **resourceType** (enum: "document", "stylesheet", "image", "media", "font", "script", "texttrack", "xhr", "fetch", "prefetch", "eventsource", "websocket", "manifest", "signedexchange", "ping", "cspviolationreport", "preflight", "fedcm", "other") _(optional)_: Only override requests of this resource type. When omitted, all resource types can match.
+- **responseFilePath** (string) _(optional)_: Local file to serve as the response. The file is read again for every matching request so rebuilds are picked up. Exactly one of responseFilePath or redirectUrl is required.
+
+---
+
 ### `get_network_request`
 
 **Description:** Gets a network request by an optional reqid, if omitted returns the currently selected request in the DevTools Network panel.
@@ -331,6 +348,14 @@
 
 ---
 
+### `list_network_overrides`
+
+**Description:** Lists the network overrides configured for the selected page.
+
+**Parameters:** None
+
+---
+
 ### `list_network_requests`
 
 **Description:** List all requests for the currently selected page since the last navigation.
@@ -344,6 +369,16 @@
 
 ---
 
+### `remove_network_override`
+
+**Description:** Removes a network override from the selected page.
+
+**Parameters:**
+
+- **id** (integer) **(required)**: ID returned by [`add_network_override`](#add_network_override).
+
+---
+
 ## Debugging
 
 ### `evaluate_script`

scripts/eval_scenarios/network_override_local_file_test.ts

@@ -0,0 +1,42 @@
+/**
+ * @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:
+    'Open the website at <TEST_URL> and replace the script named my-third-party.js using my local JavaScript file at /my-third-party-local.js.',
+  maxTurns: 4,
+  htmlRoute: {
+    path: '/network_override_local_file_test.html',
+    htmlContent: `
+      <h1>Local network override test</h1>
+      <script src="/my-third-party.js"></script>
+    `,
+  },
+  expectations: result => {
+    const pageId = result.consumePageNavigation();
+    const overrideCall = result.remainingCalls.find(
+      call => call.name === 'add_network_override',
+    );
+    assert.ok(
+      overrideCall,
+      `Expected add_network_override after navigation, got: ${result.remainingCalls.map(call => call.name).join(', ')}`,
+    );
+    assert.strictEqual(overrideCall.args.urlPattern, '*my-third-party.js*');
+    assert.strictEqual(overrideCall.args.resourceType, 'script');
+    assert.strictEqual(
+      overrideCall.args.responseFilePath,
+      '/my-third-party-local.js',
+    );
+    assert.strictEqual(overrideCall.args.redirectUrl, undefined);
+    if (result.hasPageIdRouting) {
+      assert.strictEqual(overrideCall.args.pageId, pageId);
+    }
+  },
+};

scripts/eval_scenarios/network_override_redirect_test.ts

@@ -0,0 +1,42 @@
+/**
+ * @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:
+    'Open the website at <TEST_URL> and replace the script named my-third-party.js with the script hosted at https://www.examplescripts.agi/another.js.',
+  maxTurns: 4,
+  htmlRoute: {
+    path: '/network_override_redirect_test.html',
+    htmlContent: `
+      <h1>Redirect network override test</h1>
+      <script src="/my-third-party.js"></script>
+    `,
+  },
+  expectations: result => {
+    const pageId = result.consumePageNavigation();
+    const overrideCall = result.remainingCalls.find(
+      call => call.name === 'add_network_override',
+    );
+    assert.ok(
+      overrideCall,
+      `Expected add_network_override after navigation, got: ${result.remainingCalls.map(call => call.name).join(', ')}`,
+    );
+    assert.strictEqual(overrideCall.args.urlPattern, '*my-third-party.js*');
+    assert.strictEqual(overrideCall.args.resourceType, 'script');
+    assert.strictEqual(
+      overrideCall.args.redirectUrl,
+      'https://www.examplescripts.agi/another.js',
+    );
+    assert.strictEqual(overrideCall.args.responseFilePath, undefined);
+    if (result.hasPageIdRouting) {
+      assert.strictEqual(overrideCall.args.pageId, pageId);
+    }
+  },
+};

skills/chrome-devtools-cli/SKILL.md

@@ -101,6 +101,10 @@ chrome-devtools list_network_requests # List all network requests
 chrome-devtools list_network_requests --pageSize 50 --pageIdx 0 # List network requests with pagination
 chrome-devtools list_network_requests --resourceTypes Fetch # Filter requests by resource type
 chrome-devtools list_network_requests --includePreservedRequests true # Include preserved requests
+chrome-devtools add_network_override --urlPattern 'https://example.com/app.js*' --resourceType script --redirectUrl 'https://dev.example.com/app.js'
+chrome-devtools add_network_override --urlPattern 'https://example.com/app.js*' --resourceType script --responseFilePath /absolute/path/to/app.js
+chrome-devtools list_network_overrides
+chrome-devtools remove_network_override --id 1
 ```
 
 ## Debugging & Inspection

skills/chrome-devtools/SKILL.md

@@ -29,6 +29,28 @@ Addional tooling can be enabled by providing the following flags:
 - Use pagination (`pageIdx`, `pageSize`) and filtering (`types`) to minimize data
 - Set `includeSnapshot: false` on input actions unless you need updated page state
 
+### Testing with a network override
+
+Use network overrides when a production page should load a development resource
+without changing the production HTML:
+
+1. Call `add_network_override` before the target navigation or reload.
+2. Provide `urlPattern` and exactly one action:
+   - `redirectUrl` to load another HTTP(S) URL.
+   - `responseFilePath` to fulfill the request from a local file.
+3. Restrict the rule with `resourceType` when possible, for example `script`.
+4. Navigate or reload, then use `list_network_requests` and page behavior to
+   verify the replacement.
+5. Call `list_network_overrides` to inspect active rules and
+   `remove_network_override` when the experiment is complete.
+
+Overrides are scoped to the selected page, persist across its navigations, and
+are removed when that page closes. Newer matching rules take precedence. Local
+files are read again for every match, so a rebuild is picked up on the next
+reload. Service-worker-generated responses can bypass network interception.
+Changed script bytes still fail an incompatible Subresource Integrity hash, and
+cross-origin redirects remain subject to CSP and CORS.
+
 ### Tool selection
 
 - **Automation/interaction**: `take_snapshot` (text-based, faster, better for automation)

src/McpContext.ts

@@ -756,6 +756,15 @@ export class McpContext implements Context {
     throw new Error(`Not allowed by allowlist: ${url}`);
   }
 
+  validateNetworkUrl(url: string): void {
+    const parsedUrl = new URL(url);
+    if (parsedUrl.protocol !== 'https:' && parsedUrl.protocol !== 'http:') {
+      throw new Error('Unsupported URL protocol: ' + parsedUrl.protocol);
+    }
+    this.#validateUrlNotBlocked(parsedUrl);
+    this.#validateUrlAllowed(parsedUrl);
+  }
+
   async loadResource(path: string): Promise<string> {
     const url = new URL(path);
 

src/McpPage.ts

@@ -59,6 +59,11 @@ import {
   createTargetUniverse,
   type TargetUniverse,
 } from './devtools/DevtoolsUtils.js';
+import {
+  NetworkOverrideManager,
+  type NetworkOverride,
+  type NetworkOverrideInput,
+} from './NetworkOverrideManager.js';
 import {
   ConsoleCollector,
   NetworkCollector,
@@ -137,6 +142,7 @@ export class McpPage implements ContextPage {
 
   #hasNetworkBlockOrAllowlist: boolean;
   #locatorClass: typeof Locator;
+  #networkOverrideManager: NetworkOverrideManager;
 
   constructor(
     page: Page,
@@ -150,6 +156,7 @@ export class McpPage implements ContextPage {
     this.#hasNetworkBlockOrAllowlist = options.hasNetworkBlockOrAllowlist;
     this.#locatorClass = options.locatorClass;
     this.pptrPage = page;
+    this.#networkOverrideManager = new NetworkOverrideManager(page);
     this.id = id;
     this.isolatedContextName = options.isolatedContextName;
     this.#dialogHandler = (dialog: Dialog): void => {
@@ -424,10 +431,23 @@ export class McpPage implements ContextPage {
 
   dispose(): void {
     this.pptrPage.off('dialog', this.#dialogHandler);
+    void this.#networkOverrideManager.dispose();
     this.networkCollector.dispose();
     this.consoleCollector.dispose();
   }
 
+  addNetworkOverride(input: NetworkOverrideInput): Promise<NetworkOverride> {
+    return this.#networkOverrideManager.add(input);
+  }
+
+  listNetworkOverrides(): NetworkOverride[] {
+    return this.#networkOverrideManager.list();
+  }
+
+  removeNetworkOverride(id: number): Promise<boolean> {
+    return this.#networkOverrideManager.remove(id);
+  }
+
   async executeThirdPartyDeveloperTool(
     toolName: string,
     params: Record<string, unknown>,