Chrome DevTools MCP

/** * @license * Copyright 2025 Google LLC * SPDX-License-Identifier: Apache-2.0 */ import type {JSHandle} from 'puppeteer-core'; import z from 'zod'; import {ToolCategories} from './categories.js'; import {defineTool} from './ToolDefinition.js'; export const evaluateScript = defineTool({ name: 'evaluate_script', description: `Evaluate a JavaScript function inside the currently selected page. Returns the response as JSON so returned values have to JSON-serializable.`, annotations: { category: ToolCategories.DEBUGGING, readOnlyHint: false, }, schema: { function: z.string().describe( `A JavaScript function to run in the currently selected page. Example without arguments: \`() => { return document.title }\` or \`async () => { return await fetch("example.com") }\`. Example with arguments: \`(el) => { return el.innerText; }\` `, ), args: z .array( z.object({ uid: z .string() .describe( 'The uid of an element on the page from the page content snapshot', ), }), ) .optional() .describe(`An optional list of arguments to pass to the function.`), }, handler: async (request, response, context) => { const page = context.getSelectedPage(); const fn = await page.evaluateHandle(`(${request.params.function})`); const args: Array<JSHandle<unknown>> = [fn]; try { for (const el of request.params.args ?? []) { args.push(await context.getElementByUid(el.uid)); } await context.waitForEventsAfterAction(async () => { const result = await page.evaluate( async (fn, ...args) => { // @ts-expect-error no types. return JSON.stringify(await fn(...args)); }, ...args, ); response.appendResponseLine('Script ran on page and returned:'); response.appendResponseLine('```json'); response.appendResponseLine(`${result}`); response.appendResponseLine('```'); }); } finally { Promise.allSettled(args.map(arg => arg.dispose())).catch(() => { // Ignore errors }); } }, });