BrowserChatBridge (bcb) — ChatGPT & Gemini as Claude Code tools

A Claude Code plugin that lets Claude talk to your signed-in ChatGPT and Gemini browser tabs. No API keys, no scraping services: a tiny browser extension types into the real web UI and reads the reply back.

Claude Code ──MCP stdio──► mcp-server ──WebSocket (127.0.0.1:17361)──► browser extension ──► chatgpt.com / gemini.google.com tabs

Tools exposed to Claude:

Plus two slash commands, /bcb:setup and /bcb:doctor, and a skill that teaches Claude when to reach for a second opinion.

Install

Requires Node 20+ and a Chromium browser (Chrome, Edge, Brave).

claude plugin marketplace add satabd/BrowserChatBridge-Plugin
claude plugin install bcb@bcb

Or, for a local checkout:

claude --plugin-dir /path/to/BrowserChatBridge-Plugin

Then, inside Claude Code, run /bcb:setup once. It stages the extension in a stable folder, opens your browser's extensions page, and walks you through the single manual step: Developer mode → Load unpacked → pick the folder. Sign in to chatgpt.com and gemini.google.com and you're done.

Try it: "Ask ChatGPT what it thinks of this function."

Related MCP server: MCP Browser Extension

How it works (and why it's robust)

• Extension is the WebSocket client, so it reconnects on its own when a Claude Code session starts. A chrome.alarms heartbeat keeps the MV3 service worker from sleeping through it.

• Many sessions, one extension. Each Claude Code session spawns its own MCP server. The first to bind port 17361 becomes the leader; the rest proxy to it over loopback HTTP. If the leader exits, the next call re-elects.

• Composer input uses focus → execCommand('selectAll') → execCommand('insertText') plus a synthetic InputEvent. Setting textContent does not update ProseMirror (ChatGPT) or Quill (Gemini) state.

• Completion is a hybrid gate: provider "generating" signals (ChatGPT's Stop button and data-talvt-turn-state, Gemini's aria-busy / .pending) and user+assistant turn counts past a pre-send baseline and the extracted text unchanged for 2.5 s. Stop-button-alone is racy.

• Selectors are fallback chains, newest first, in extension/src/content/adapters/. When a site redesigns, add a new first entry; don't delete the old ones.

• Gemini quirk: replies only finalise once the tab paints. The extension activates the target tab for the duration of an ask.

• Everything binds to 127.0.0.1 only. Prompts go to your own ChatGPT/Gemini account exactly as if you typed them.

Repo layout

.claude-plugin/plugin.json    plugin manifest (name: bcb)
.claude-plugin/marketplace.json  single-plugin marketplace so `claude plugin install bcb@bcb` works
.mcp.json                     declares the stdio MCP server (node mcp-server/dist/index.js)
mcp-server/src/               MCP tools + leader/follower bridge (bundled → mcp-server/dist, committed)
extension/src/                MV3 extension: background.ts, content/{entry,dom,markdown}.ts, adapters/{chatgpt,gemini}.ts
extension/dist/               built extension (committed; what you load unpacked)
shared/protocol.ts            wire types shared by both sides
scripts/setup.mjs             /bcb:setup helper
commands/, skills/            slash commands and the skill
tests/                        fake-extension + stdio MCP client for Node-side e2e

Develop

npm install
npm run build        # bundles extension/dist and mcp-server/dist (commit both)
npm run typecheck
node tests/fake-extension.mjs &   # pretends to be the browser
node tests/mcp-client.mjs --two   # spawns two servers: leader + follower

After changing the extension, reload it at chrome://extensions. After changing the MCP server, run /reload-plugins or restart Claude Code.

When a site changes its UI

Open the site, inspect the composer / send button / message containers, prepend the new selector to the relevant chain in extension/src/content/adapters/<provider>.ts, rebuild, reload the extension. The adapter header comments record what each selector looked like on the last verified date.

License

MIT