@businessmaps/bifrost

MCP server that lets AI tools call functions running in your browser.

The daemon sits between any MCP client and your browser tab. It speaks JSON-RPC over stdio on one side and WebSocket on the other. Your browser app connects, registers tools, and the AI can call them. No dependencies, just Node 18+.

Install

npm i -g @businessmaps/bifrost

or without npm

curl -fsSL https://raw.githubusercontent.com/Business-Maps/mcp/main/install.sh | sh

Then register it with your MCP client. For example:

claude mcp add --transport stdio bifrost -- bifrost

The MCP client starts the daemon automatically.

Usage

Install the client library in your browser app:

npm i @businessmaps/bifrost-browser

Or use a CDN:

<script src="https://unpkg.com/@businessmaps/bifrost-browser"></script>

TypeScript types are included out of the box — no @types package needed.

Then register your tools:

import { BifrostBrowser } from "@businessmaps/bifrost-browser";

const bridge = new BifrostBrowser({
  port: 3099,
  token: "TOKEN", // printed to stderr when daemon starts
});

bridge.registerTools([
  {
    name: "get_selection",
    description: "Returns the user's text selection",
    inputSchema: { type: "object", properties: {} },
    handler: async () => window.getSelection().toString(),
  },
]);

bridge.connect();

Handlers run in the browser -- full access to DOM, Canvas, IndexedDB, Clipboard, fetch, etc.

There's a working live demo with five sample tools you can try right away.

Auth

The daemon generates a token on startup and prints it to stderr. Pass it to the client — the token is sent via the Sec-WebSocket-Protocol header during the WebSocket handshake. Skip with --no-auth during local dev.

Multiple tabs

Each tab registers its own tools. Calls route to whoever owns the tool. Disconnecting a tab removes its tools.

Options

--port <port>     WebSocket port        (default: 3099)
--timeout <secs>  Tool call timeout     (default: 120)
--no-auth         Disable token auth    (dev only)
--help, -h        Show this message
--version, -v     Show version

Dev

git clone https://github.com/Business-Maps/mcp.git && cd mcp
npm test  # no install needed, no deps

Architecture · Client API · Contributing

License

Apache 2.0