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Browser-MCP Navigator

by ingjohnfigueroablanco
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Python
Hybrid

Fast-Browser-MCP (Fast-Browser-MCP Navigator)

Ultra-fast browser automation server over Chrome DevTools Protocol (CDP), exposed as a Model Context Protocol (MCP) server.

No screenshots. No Playwright relay. Direct CDP WebSocket — 20–50× fewer tokens, ~10ms per action.

Note: The core Python package is named fast_browser_mcp internally.

What it does

Controls a real Chrome browser from any AI agent that supports MCP. The agent receives a compact accessibility-tree snapshot with @eN references after every action — no pixels, no heavy HTML blobs.

Agent  ──MCP──►  Fast-Browser-MCP Server  ──CDP──►  Chrome

Related MCP server: Scout

Quick Start — Docker (Recommended)

git clone https://github.com/ingjohnfigueroablanco/Fast-browser-MCP.git
cd Fast-browser-MCP
cp .env.example .env          # optionally set MCP_API_KEY
docker compose up -d

Server ready at http://localhost:3067/sse.

Quick Start — Local (No Docker)

git clone https://github.com/ingjohnfigueroablanco/Fast-browser-MCP.git
cd Fast-browser-MCP
python -m venv .venv 
source .venv/bin/activate     # Windows: .venv\Scripts\activate
pip install -e .
python -m fast_browser_mcp  # stdio mode

Connecting from Claude Code

Option A — Local subprocess / stdio

Add to your project's .mcp.json:

{
  "mcpServers": {
    "fast-browser-mcp": {
      "command": "python",
      "args": ["-m", "fast_browser_mcp"]
    }
  }
}

Option B — Docker / SSE

{
  "mcpServers": {
    "fast-browser-mcp": {
      "type": "sse",
      "url": "http://localhost:3067/sse",
      "headers": { "X-API-Key": "your-key" }
    }
  }
}

Connecting from other agents / frameworks

Python agent (mcp SDK)

from mcp import ClientSession
from mcp.client.sse import sse_client

async with sse_client("http://localhost:3067/sse",
                      headers={"X-API-Key": "your-key"}) as (read, write):
    async with ClientSession(read, write) as session:
        await session.initialize()
        result = await session.call_tool("navigate", {"url": "https://example.com"})
        print(result.content[0].text)

Testing Localhost Apps (Docker)

The browser runs inside the container. localhost inside Docker ≠ your dev machine.

Approach

How

Docker Desktop

Use http://host.docker.internal:3000 instead of localhost:3000

ngrok

ngrok http 3000 → gives a public URL the container can reach

Local mode

(stdio) Chrome runs on your machine — localhost works normally

Available Tools

Tool

Description

browser_start

Launch / reconnect Chrome

browser_stop

Close Chrome

navigate

Go to URL, wait for load / networkidle

snapshot

Accessibility tree as compact text with @eN refs

click

Human-like click by coordinates

js_click

element.click() — reliable for React / Angular SPAs

fill

Clear + type text in an input

press_key

Key press (Enter, Tab, Escape, ArrowDown…)

select_option

Select native <select> by value or label

hover

Mouse hover (menus, tooltips)

set_value

React/Vue/Angular-safe input setter via native JS

scroll

Scroll page or element into view

js_eval

Run any JavaScript — drag, events, async fetch, bulk loops

js_eval_loop

Bulk operations — run a JS snippet once per item

cdp_call

Raw CDP protocol — file upload, device emulation, network intercept

get_text

innerText of element or full page

wait_for

Wait until text appears on page

read_console

JS console logs

read_network

Network requests / responses

screenshot

PNG base64 (escape hatch)

current_url

Current URL + title

Performance & Bulk Operations

The bottleneck is LLM round-trips, not the browser

Each tool call costs one full LLM inference + HTTP round-trip. The browser executes CDP in ~10ms.

Pattern

Tool calls

Typical wall time

20 × (click + fill + click)

60

~10 min

1 × js_eval_loop with 20 items

1

~15 sec

Rule: for N > 5 repetitions, use js_eval_loop

# GOOD — 1 tool call for 20 users
js_eval_loop(
    items=users,
    script="""
      document.querySelector('.agregar').click();
      await new Promise(r => setTimeout(r, 400));
      // ... fill logic ...
      document.querySelector('.crear').click();
      return item.user;
    """,
    delay_ms=300,
)

Environment Variables

Variable

Default

Description

MCP_TRANSPORT

stdio

stdio (local) or sse (Docker/remote)

MCP_HOST

0.0.0.0

SSE bind address

MCP_PORT

3067

SSE port

MCP_API_KEY

(empty)

API key header; empty = no auth

CHROME_PATH

auto

Explicit path to chrome.exe

CHROME_EXTRA_ARGS

(empty)

Extra Chrome flags

Fast-Browser-MCP_HEADLESS

0

1 for headless mode

Fast-Browser-MCP_HUMAN_DELAYS

1

0 removes human-like delays (faster)

Architecture

mcp/         FastMCP server + tool definitions
browser/     BrowserManager — lifecycle, navigate, snapshot, waits
snapshot/    AX tree → compact text with @eN refs (no screenshots)
actions/     mouse, keyboard, forms (ref → coordinates)
cdp/         Raw CDP WebSocket connection + event buffers
chrome/      Chrome launcher, port scan, reattach

Why it's faster than Playwright:

  • No Node.js relay — Python speaks CDP directly.

  • Chrome stays alive between calls (daemon) — 0 ms startup per tool call.

  • Snapshot = compact AX text, not full YAML or heavy screenshots.

  • @eN refs = stable backendNodeId — no DOM re-query per action.

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