Browser 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

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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

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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" }
    }
  }
}

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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)

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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

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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

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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,
)

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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)

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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.