Browser Buddy

Browser Buddy

Let your coding agent read pages through YOUR real, logged-in browser.

Claude Code's WebFetch gets 403'd on most sites. Ask it to pull up a doc, check a Reddit thread, or look at a GitHub issue, and it comes back with a 403 — because server-side fetchers don't have your cookies, your logins, or your sessions.

Browser Buddy is a small local MCP bridge: a Chrome extension (Manifest V3) talks to a Python native-messaging host, which exposes two MCP tools. Your agent reads pages exactly as you see them — logged in, past bot checks — and the page never leaves your machine except into the agent's context.

Stdlib only. No dependencies, no cloud, no API keys.

Tools

Architecture

┌─────────────┐   MCP (JSON-RPC 2.0     ┌──────────────────┐  Unix socket   ┌───────────────────┐  Native Messaging  ┌────────────────┐
│ Claude Code │ ── over stdio, NDJSON ──▶ │ browser_buddy_mcp  │ ── NDJSON ──▶ │ browser_buddy_host │ ── 4-byte LE ──▶ │ Chrome extension │
│             │ ◀────────────────────── │      .py           │ ◀──────────── │       .py          │ ◀── JSON ─────── │ (your profile) │
└─────────────┘                          └──────────────────┘                └───────────────────┘                  └────────────────┘
         ▲                                        │                                                                     │
         │                                        │  one request per socket connection;                                 │  chrome.tabs +
         └──────── page text lands here ──────────┘  host routes replies by request id                                  │  chrome.scripting
                                                                                                                        ▼
                                                                                                              real logged-in page

• Extension (extension/): MV3 service worker. Holds a persistent chrome.runtime.connectNative port to the host (auto-reconnects). Executes read_active_tab / open_and_read_url against your real tabs and posts extracted text back.
• Host (host/browser_buddy_host.py): launched by Chrome. Bridges the extension (length-prefixed stdio) and the MCP server (Unix socket at $TMPDIR/browser-buddy/browser-buddy.sock). Correlates requests by id, with a 90 s timeout.
• MCP server (pypi/browser_buddy_mcp.py): hand-rolled JSON-RPC 2.0 over stdio (no mcp package). Forwards tool calls to the host; returns page text as MCP content.

Installation

1. Load the extension

1. Open chrome://extensions, enable Developer mode.
2. Load unpacked → select the extension/ folder.
3. Copy the extension ID shown under "Browser Buddy".

2. Register the native host

cd host
./install.sh <paste-extension-id-here>

This writes com.browserbuddy.host.json into Chrome's NativeMessagingHosts directory (Linux/macOS) pointing at browser_buddy_host.py. Restart Chrome, then open the extension's service worker console — you should see [browser-buddy] native host connected.

3. Add the MCP server to Claude Code

claude mcp add browser-buddy -- python3 /absolute/path/to/pypi/browser_buddy_mcp.py

Or in ~/.claude.json / project .mcp.json:

{
  "mcpServers": {
    "browser-buddy": {
      "command": "python3",
      "args": ["/absolute/path/to/browser-buddy/pypi/browser_buddy_mcp.py"]
    }
  }
}

Requires Python 3.9+. No pip install needed — or install the published package: pip install browser-buddy-mcp (built from pypi/; the browser-buddy-mcp command is the entry point).

Demo

1. Log in to a site WebFetch can't reach in your normal Chrome (e.g. a private GitHub issue, a login-walled doc).
2. In Claude Code: "Use browser-buddy to read my active tab."
3. Or: "Use browser-buddy's open_and_read_url to read ." — a background tab opens, the text is extracted, the tab closes itself.

Why not just use a scraping API? (Firecrawl et al.)

Vendor scrapers (Firecrawl, etc.) fetch pages server-side: they never have your cookies, can't get past SSO/2FA/login walls, can't see what you see behind an account, and they charge per page. The official Claude in Chrome goes the other way — full autonomous browser control — but ships a permission dialog per tool call (dozens per session) and sits at 2.7 stars on the Chrome Web Store.

Browser Buddy picks the middle: read-only access through the browser you already logged into. No credentials leave your machine, nothing to pay per page, no dialog spam — just "let the agent see what I see."

Limitations (honest)

• Chrome/Chromium only. The extension is the whole trick; no Chrome, no tool.
• Read-only by design. It extracts text; it doesn't click, type, or fill forms. That's a feature for trust, but it means CAPTCHAs / interactive gates still stop it.
• Text extraction is heuristic, not a full readability engine. Heavy SPAs usually work (we wait for load + a settle beat), but exotic layouts may extract noise.
• Your real profile = real risk surface. The agent sees everything your browser can see. Only install this if you trust the agent session reading your tabs.
• MV3 service workers are ephemeral. The extension auto-reconnects its native port, but a cold start can add ~1 s to the first call.
• One request at a time per socket connection is fine for an agent; this is not built for concurrent scraping fleets.
• Long pages are truncated at 60k characters (flagged with (truncated)).

Security: domain allowlist

open_and_read_url opens URLs in your real, logged-in browser. A prompt-injected page could otherwise steer the agent toward your email or other sensitive sites. Restrict which domains the agent may open:

// ~/.config/browser-buddy/config.json
{
  "allowed_domains": ["github.com", "stackoverflow.com"]
}

Entries match the domain and its subdomains (docs.github.com is covered by github.com). When the list is empty (default), any URL is allowed but the server logs a warning recommending you set it. URLs outside the list are refused before anything is opened. read_active_tab is unaffected — it only reads the tab you already opened.

Development

python3 tests/test_smoke.py   # 25 tests: framing, bridge routing, MCP handlers,
                              # socket dir, domain allowlist
node --check extension/background.js

License

MIT — see LICENSE.