Features
Local Servers
Most MCP servers in the registry are stdio-based packages meant for local use. Here's how to expose them over HTTP so you can test them in MCP Playground.
Why can't I connect directly?
MCP Playground connects to remote servers over HTTP or WebSocket (Streamable HTTP, SSE, or WebSocket transport). Stdio-based servers communicate through standard input/output and need a local process to bridge them to HTTP. This is by design — running arbitrary processes in the browser would be a security risk.
Option 1: supergateway (recommended)
supergateway wraps any stdio MCP server and exposes it as an SSE endpoint with one command.
Install globally
npm install -g supergatewayRun any stdio server over SSE (example: filesystem server)
npx supergateway --stdio 'npx -y @modelcontextprotocol/server-filesystem /tmp' --port 3001Then connect in MCP Playground
http://localhost:3001/sseOption 2: mcp-proxy (Python)
mcp-proxy is a Python tool that bridges stdio servers to SSE.
Install
pip install mcp-proxyRun a server with SSE transport
mcp-proxy --sse-port 3001 -- npx -y @modelcontextprotocol/server-filesystem /tmpOption 3: Servers with built-in HTTP
Some servers already support HTTP transport natively. Check the server's README for flags like --transport sse or --transport http.
Example: a server with built-in SSE support
npx -y some-mcp-server --transport sse --port 3001Tips
- 1.Make sure the port isn't blocked by your firewall.
- 2.MCP Playground's SSRF protection blocks localhost in production. Use it locally during development.
- 3.For testing, we include a built-in test server: run
pnpm test-serverin this repo.