# 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 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: `/sse` for SSE server, `/stream` for stream server)
- `--server`: Specify the server type to use (default: `sse`)
- `--debug`: Enable debug logging
### 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();
```
#### `startHTTPStreamServer`
Starts a proxy that listens on a `port` and `endpoint`, and sends messages to the attached server via `StreamableHTTPServerTransport`.
```ts
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();
```
#### `startStdioServer`
Starts a proxy that listens on a `stdio`, and sends messages to the attached `sse` or `streamable` server.
```ts
import { ServerType, startStdioServer } from "./startStdioServer.js";
await startStdioServer({
serverType: ServerType.SSE,
url: "http://127.0.0.1:3000/sse",
});
```
#### `tapTransport`
Taps into a transport and logs events.
```ts
import { tapTransport } from "mcp-proxy";
const transport = tapTransport(new StdioClientTransport(), (event) => {
console.log(event);
});
```
