mcp-proxy

# MCP Proxy A TypeScript SSE proxy for [MCP](https://modelcontextprotocol.io/) servers that use `stdio` transport. > [!NOTE] > CORS is enabled by default. > [!NOTE] > For a Python implementation, see [mcp-proxy](https://github.com/sparfenyuk/mcp-proxy). > [!NOTE] > MCP Proxy is what [FastMCP](https://github.com/punkpeye/fastmcp) uses to enable SSE. ## Installation ```bash npm install mcp-proxy ``` ## Quickstart ### Command-line ```bash npx mcp-proxy --port 8080 --endpoint /sse tsx server.js ``` This starts an SSE server and `stdio` server (`tsx server.js`). The SSE server listens on port 8080 and endpoint `/sse`, and forwards messages to the `stdio` server. ### Node.js SDK The Node.js SDK provides several utilities that are used to create a proxy. #### `proxyServer` Sets up a proxy between a server and a client. ```ts const transport = new StdioClientTransport(); const client = new Client(); const server = new Server(serverVersion, { capabilities: {}, }); proxyServer({ server, client, capabilities: {}, }); ``` In this example, the server will proxy all requests to the client and vice versa. #### `startSSEServer` Starts a proxy that listens on a `port` and `endpoint`, and sends messages to the attached server via `SSEServerTransport`. ```ts import { Server } from "@modelcontextprotocol/sdk/server/index.js"; import { startSSEServer } from "mcp-proxy"; const { close } = await startSSEServer({ port: 8080, endpoint: "/sse", createServer: async () => { return new Server(); }, }); close(); ``` #### `tapTransport` Taps into a transport and logs events. ```ts import { tapTransport } from "mcp-proxy"; const transport = tapTransport(new StdioClientTransport(), (event) => { console.log(event); }); ```