A TypeScript SSE proxy for MCP servers that use stdio transport.
Note
CORS is enabled by default.
Note
For a Python implementation, see mcp-proxy.
Note
MCP Proxy is what FastMCP uses to enable SSE.
npm install mcp-proxynpx mcp-proxy --port 8080 --endpoint /sse tsx server.jsThis starts a server and stdio server (tsx server.js). The server listens on port 8080 and endpoint /sse by default, and forwards messages to the stdio server.
options:
--port: Specify the port to listen on (default: 8080)--endpoint: Specify the endpoint to listen on (default:/ssefor SSE server,/streamfor stream server)--server: Specify the server type to use (default:sse)--debug: Enable debug logging
The Node.js SDK provides several utilities that are used to create a proxy.
Sets up a proxy between a server and a client.
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.
Starts a proxy that listens on a port and endpoint, and sends messages to the attached server via SSEServerTransport.
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();Starts a proxy that listens on a port and endpoint, and sends messages to the attached server via StreamableHTTPServerTransport.
import { Server } from "@modelcontextprotocol/sdk/server/index.js";
import { startHTTPStreamServer, InMemoryEventStore } from "mcp-proxy";
const { close } = await startHTTPStreamServer({
port: 8080,
endpoint: "/stream",
createServer: async () => {
return new Server();
},
eventStore: new InMemoryEventStore(), // optional you can provide your own event store
});
close();Starts a proxy that listens on a stdio, and sends messages to the attached sse or streamable server.
import { ServerType, startStdioServer } from "./startStdioServer.js";
await startStdioServer({
serverType: ServerType.SSE,
url: "http://127.0.0.1:3000/sse",
});Taps into a transport and logs events.
import { tapTransport } from "mcp-proxy";
const transport = tapTransport(new StdioClientTransport(), (event) => {
console.log(event);
});