BrowserTools MCP

BrowserTools MCP

Give your AI coding agent eyes on the browser. BrowserTools MCP streams console

output, network activity, screenshots and Lighthouse audits from **your real

Chrome session** — the one already logged into your app — to any MCP-compatible

client: Cursor, Claude Code, Windsurf, Cline, Zed, Gemini CLI, and others.

Version 2.0 is a rewrite. One process instead of three, no unauthenticated

local server, credentials scrubbed before they leave the browser, and a real

test suite. If you are coming from 1.x, read MIGRATION.md ↗ —

and upgrade, because 1.2.x has a critical vulnerability. See

SECURITY.md ↗.

Why this instead of a CDP-based server

Tools like Chrome DevTools MCP and Playwright MCP drive a *fresh, automated*

browser. That is the right choice for writing tests. It is the wrong choice for

debugging the app you are actually looking at, because since Chrome 136 the

browser refuses remote debugging on your default profile — the one holding your

logins. So you end up recreating your auth state in a throwaway profile before

you can debug anything.

BrowserTools attaches to the session you are already in, through a DevTools

extension. You stay logged in, on the page you were already on, and your agent

reads what you see. It also reports Lighthouse-grade performance, accessibility

and SEO data, which the automation-first servers do not.

Install

Two pieces: an MCP server (one command) and a Chrome extension.

1. Point your MCP client at the server

{
  "mcpServers": {
    "browser-tools": {
      "command": "npx",
      "args": ["-y", "@agentdeskai/browser-tools-mcp@latest"]
    }
  }
}

On Windows, if your client cannot find npx, use "command": "cmd" with

"args": ["/c", "npx", "-y", "@agentdeskai/browser-tools-mcp@latest"].

Requires Node 22.19 or newer. Check with node --version; if you use nvm or

asdf, make sure your editor inherits the same version.

2. Load the Chrome extension

• Download or clone this repository.
• Open chrome://extensions and turn on Developer mode.
• Choose Load unpacked and select the chrome-extension directory.

That is the whole setup. There is no second server to start — the MCP server

runs the connector itself.

3. Use it

Open Chrome DevTools (F12) on the page you want to inspect. Capture begins as

soon as DevTools is open; the BrowserTools panel is only for settings and

status. Then ask your agent something like *"check the console for errors"* or

*"run an accessibility audit on this page"*.

Not working? Run npx @agentdeskai/browser-tools-mcp --doctor, which reports

exactly which piece is missing.

To watch capture happen live — useful when checking a fresh install — start the

connector with --verbose:

npx @agentdeskai/browser-tools-server --verbose

· console error tab 42 Uncaught TypeError: total is not a function
· network 500 POST tab 42 https://myapp.local/api/pay (1310ms)

Without it the connector only reports connect and disconnect, so a working

setup and a silent one look the same.

Tools

· Tool · What it does ·

· getConsoleLogs · Console output, filterable by keyword with paging ·

· getConsoleErrors · Error-level output and uncaught exceptions ·

· getNetworkLogs · XHR/fetch requests with status, timing and bodies ·

· getNetworkErrors · Only failed and 4xx/5xx requests ·

· getSelectedElement · The element selected in the Elements panel ·

· getPageInfo · Which page the browser is currently on ·

· getConnectionStatus · Whether the extension is connected, and capture counts ·

· listBrowserTabs · Every tab with DevTools open, and the id to address it by ·

· takeScreenshot · Screenshot returned as an image, plus its file path ·

· refreshBrowser · Reloads the inspected tab ·

· getBrowserStorage · localStorage, sessionStorage and cookies (values gated) ·

· wipeLogs · Clears captured telemetry before a clean reproduction ·

· runAccessibilityAudit · Lighthouse accessibility audit ·

· runPerformanceAudit · Lighthouse performance audit with Core Web Vitals ·

· runSEOAudit · Lighthouse SEO audit ·

· runBestPracticesAudit · Lighthouse best-practices audit ·

Three prompts ship alongside them — debuggerMode, auditMode and

nextjsSeoAudit — giving your agent a systematic workflow instead of a wall of

static text in every tool listing.

All tools declare MCP output schemas, so clients receive structured data rather

than prose they have to parse, and read-only tools are annotated as such so

clients can auto-approve them safely.

Several tabs at once

Every tab with DevTools open is tracked separately. Telemetry is attributed to

the tab that produced it, and retention is per tab, so a chatty page cannot push

out the history of the one you care about.

Tools act on the current tab — the one you most recently opened DevTools on.

A tab whose connection drops and comes back does not steal that position, which

is what used to make screenshots capture the wrong page. Every result reports

the tabId and url it came from, plus otherTabs, so a wrong-tab answer is

visible rather than silent. To target a specific tab, call listBrowserTabs and

pass its tabId to any tool; pass allTabs: true to read across every tab.

Large data stays out of the context window

Whole-history payloads are exposed as MCP resources rather than inlined, and

tools link to them with resource_link so your agent fetches them only when it

decides to:

· Resource · What it is ·

· browser-tools://console/{tabId\ · all} · Every console entry, with no per-call budget ·

· browser-tools://network/{tabId\ · all} · Every captured request, including bodies ·

· browser-tools://har/{tabId\ · all} · The same traffic as a HAR 1.2 file ·

· browser-tools://screenshot/{name} · A screenshot you captured earlier ·

· browser-tools://audit/{reportId} · The unabridged Lighthouse result behind a summary ·

Log tools attach a link when a read had to be cut short; network reads always

offer the HAR; screenshots always link to the stored image, which is the only

way to see one too large to inline. The last 20 full Lighthouse reports are kept

under audits/ in the screenshot directory.

Keeping responses small

Log payloads are the usual cause of a blown context window. Every read tool

takes limit and offset, and the log tools take keyword filters:

getConsoleErrors({ keywords: ["hydration"], limit: 20 })
getNetworkLogs({ urlKeywords: ["/api/"], bodyKeywords: ["quota"], limit: 10 })

Results are returned newest-first and always report total alongside

returned, so an agent knows when it is only seeing part of the picture.

Privacy and security

This tool captures whatever your browser sees, so it treats that data carefully:

• Loopback only. The connector binds 127.0.0.1 and refuses non-loopback

addresses. In 1.x it bound 0.0.0.0, reachable by anyone on your network.

• The extension never leaves loopback. 1.x scanned private network ranges

and adopted whichever host answered with a known string — meaning anyone on

shared Wi-Fi could receive your logs and screenshots. That scan is gone.

• Authenticated. The HTTP API requires a per-run token. The WebSocket

accepts browser-extension origins only, so a web page you visit cannot

impersonate the extension.

• Credentials are scrubbed on the way in: Authorization, Cookie and

similar headers, plus JWTs, cloud keys and vendor tokens found anywhere in

captured strings, become [REDACTED].

• Headers are off by default, per direction, and storage values are withheld

unless explicitly requested.

• Cookie access is an optional permission you grant from the panel, not

something the extension holds by default.

• Audits stay off your internal network. An audit accepts a url, and the

caller may be a model reading untrusted pages. Link-local and cloud metadata

addresses are never audited. Pages on localhost or a private network are

audited only while open in a connected tab (or allowlisted with

--audit-allow-origin), and every request the audit browser makes —

redirects and subresources included — is checked again as it happens. A

local page may load only the local origins that are open in a tab or

allowlisted, so if your app calls an API on another local port, open that

too or allowlist it. Audits connect directly, not through a system proxy.

Behind a fake-IP proxy (Clash, sing-box, Surge), which hides where names

really go, audits are refused unless you pass

--audit-allow-private-network; see SECURITY.md.

Report vulnerabilities per SECURITY.md ↗.

Configuration

Flags, or the matching BROWSER_TOOLS_* environment variables:

· Flag · Purpose ·

· --port <n> · Connector port (default 3025) ·

· --screenshot-dir <path> · Where screenshots are written ·

· --only · Expose only these tools ·

· --exclude · Hide these tools ·

· --doctor · Check the setup and exit ·

· --verbose · Print each captured entry as it arrives ·

· --host <addr> · Loopback address to bind (default 127.0.0.1) ·

· --connect <url> · Attach to a connector already running elsewhere ·

· --token <t> · Auth token to use with --connect ·

· --no-redact · Disable credential scrubbing (not recommended) ·

· --audit-allow-origin <o,o> · Loopback/private origins audits may target or load without an open tab ·

· --audit-allow-private-network · Let audits reach any loopback/private address except the audit's own ports (not recommended); also needed behind a fake-IP proxy ·

To share one browser session between several MCP clients, start the connector

once with npx @agentdeskai/browser-tools-server and every client will attach to

it automatically.

Known limits

• Network capture starts when DevTools opens. Requests that finished before then

are not recorded — reload the page to capture a full page load.

• Screenshots are held to a byte budget (screenshotMaxBytes, 3 MB by default).

A capture that would exceed it is re-encoded as JPEG and, if still too large,

downscaled. A viewport capture of dense content on a high-DPI display can

otherwise run past 13 MB, which is more than a model's context can take and

past the read buffer newer MCP stdio transports enforce. If an image still

cannot fit, it is written to disk and the tool returns the path instead of

inlining it.

• Console capture defaults to the DevTools protocol, which makes Chrome show a

"started debugging this browser" banner. Switch the panel's capture mode to

Wrap page console to avoid it.

• Firefox is not verified. The extension is written cross-browser — a

browser/chrome shim, browser_specific_settings, and a capture mode that

does not need chrome.debugger — but it has never been loaded in Firefox, and

nothing in the test suite covers it. Screenshots in particular go through the

DevTools protocol and will not work there. Treat Firefox as unsupported until

someone has actually run it; a report either way is welcome.

• Audits launch a separate browser and take up to a minute. Any Chromium-based

browser works — Chrome, Chromium, Brave, Edge, Vivaldi, Opera or Arc — and

--doctor reports which one will be used. Set CHROME_PATH to override.

Arc is supported on a best-effort basis and has not been verified headless.

Development

npm install
npm run build
npm test           # unit + integration, no browser required
npm run test:e2e   # real Chromium with the extension loaded

npm test runs in seconds. The end-to-end suite launches a headed Chromium with

the extension installed, drives fixture pages, and asserts the whole capture

path — run npx playwright install chromium first.

License

MIT