mcp-proxy

A Rust bidirectional MCP proxy supporting SSE and Streamable HTTP transports with OAuth.

Features

• Multiple transports: SSE and Streamable HTTP
• OAuth authentication: Full OAuth flow with automatic token refresh
• Bidirectional proxy: Connect remote servers to local clients or expose local servers remotely
• Fast and lightweight: Built in rust for performance

Usage

Installing

# from crates.io
cargo install rmcp-proxy
# from github
cargo install --git https://github.com/stephenlacy/mcp-proxy

Building

cargo build --release

Running

The proxy can operate in two modes:

1. Remote Client Mode

Connect to a remote MCP server and expose it as a local stdio server. Supports both SSE and Streamable HTTP transports with automatic detection.

Transport Detection:

• URLs containing /sse → Uses SSE transport
• All other URLs → Uses Streamable HTTP transport
• Override with --transport flag

Basic Examples

# Streamable HTTP
mcp-proxy http://localhost:9090/mcp/instances_abc123

# SSE transport
mcp-proxy http://localhost:8080/sse
mcp-proxy --transport sse http://localhost:8080/events

# Specific
mcp-proxy --transport streamable-http http://localhost:9090/api

Using with Claude or Cursor

{
  "mcpServers": {
    "my-remote-server": {
      "command": "mcp-proxy",
      "args": ["http://example.com/mcp/instances_abc123"]
    },
    "sse-server": {
      "command": "mcp-proxy", 
      "args": ["--transport", "sse", "http://example.com/sse"]
    }
  }
}

2. Local Server Mode

Connect to a local MCP server via stdio and expose it as a remote server. Supports both SSE and Streamable HTTP endpoints.

# Expose as SSE server
mcp-proxy --port 8080 -- your-command --arg1 value1 --arg2 value2
mcp-proxy --port 8080 python mcp_server.py
mcp-proxy --port 8080 -- npx -y @modelcontextprotocol/server-everything

# Or http+streamable
mcp-proxy --port 9090 --transport streamable-http -- python mcp_server.py

mcp-proxy --port 8080 -e KEY VALUE -e ANOTHER_KEY ANOTHER_VALUE -- your-command

Authentication Management

Clearing Auth Cache

If you encounter authentication issues, clear the auth cache:

# Clear all auth data
mcp-proxy reset

# Or manually delete the directory
rm -rf ~/.mcp-auth

Command Line Options

# Transport selection
--transport <TRANSPORT>    # sse, streamable-http, or auto (default: auto)

# Server mode options
--port <PORT>             # Port for local server mode (default: random)
--host <HOST>             # Host to bind to (default: 127.0.0.1)

# Environment variables (server mode)
-e, --env <KEY> <VALUE>   # Set environment variable
--pass-environment        # Pass through all environment variables

# Headers (client mode) 
-H, --headers <KEY> <VALUE>  # Add custom headers

# Reset auth
mcp-proxy reset           # Clear all stored auth data

Logging

The upstream rmcp crate dumps noisy logs unfortunately

Control log verbosity with the RUST_LOG environment variable:

# Minimal logging
RUST_LOG=error mcp-proxy http://example.com/mcp
RUST_LOG=debug mcp-proxy http://example.com/mcp
RUST_LOG=info mcp-proxy http://example.com/mcp

Library Usage

use rmcp_proxy::{
    sse_client::run_sse_client,
    streamable_http_client::run_streamable_http_client,
    StreamableHttpClientConfig, SseClientConfig
};

// Streamable HTTP client
let config = StreamableHttpClientConfig {
    url: "http://example.com/mcp/instances_abc123".to_string(),
    headers: HashMap::new(),
};
run_streamable_http_client(config).await?;

// SSE client  
let config = SseClientConfig {
    url: "http://example.com/sse".to_string(),
    headers: HashMap::new(),
};
run_sse_client(config).await?;

License

MIT