MCPGate

What is MCPGate?

MCPGate creates a resilient bidirectional bridge between standard I/O and HTTP, enabling any application to communicate with MCP servers. It handles all the complexity of connection management, session persistence, and error recovery.

Built on the official @modelcontextprotocol/sdk, MCPGate provides a robust implementation of the MCP client specification with enhanced reliability features.

graph LR
    A[Your Application] -->|JSON-RPC via stdin| B[MCPGate]
    B -->|HTTP POST| C[MCP Server]
    C -->|Server-Sent Events| B
    B -->|JSON-RPC via stdout| A
    style B fill:#f9f,stroke:#333,stroke-width:2px

Features

• ⚡ Reliable Communication - Stable bridge between stdin/stdout and HTTP/SSE
• 🔄 Smart Reconnection - Automatic recovery from network issues and session timeouts
• 🔐 Session Management - Preserves sessions when possible, graceful fallbacks when not
• 📋 Message Queuing - No messages lost during connection interruptions
• 🚦 Intelligent Error Handling - Different strategies for different error types
• 📦 Lightweight - Minimal dependencies, focused functionality

Installation

# Install globally via npm
npm install -g mcpgate

# Or use without installation via npx
npx mcpgate http://example.com:8000/sse

Usage

Basic Command

mcpgate <server-url>

With Options

mcpgate http://example.com:8000/sse --debug --reconnect-delay=2000 --max-reconnects=10

In an MCP Client Configuration

{
  "mcpServers": {
    "your-servername": {
      "command": "npx",
      "args": ["-y", "mcpgate", "http://example.com:8000/sse"]
    }
  }
}

How It Works

MCPGate establishes and maintains the complex bidirectional connection required by the Model Context Protocol:

1. Connection Setup

   • Creates an SSE connection to receive server messages
   • Obtains the endpoint URL for sending messages via POST

2. Message Handling

   • Reads JSON-RPC messages from stdin
   • Queues messages when connection isn't ready
   • Sends messages to server via HTTP POST
   • Receives responses via SSE and forwards to stdout

3. Advanced Reconnection

   • Detects connection failures through multiple signals
   • Uses exponential backoff for reconnection attempts
   • Preserves original session ID when possible
   • Falls back to new session when necessary
   • Re-executes handshake sequence after reconnection

Examples

Simple Pipe

echo '{"jsonrpc":"2.0","method":"chat","params":{"message":"Hello"},"id":1}' | mcpgate http://localhost:8000/sse

Integration with Tools

# Use with a custom client
my-mcp-client | mcpgate http://example.com:8000/sse | result-processor

Debugging

# Save logs to a file while using the bridge
mcpgate http://example.com:8000/sse 2> mcpgate.log

Technical Details

Architecture

MCPGate uses a clean module pattern with clear separation of concerns:

• Connection Management - Transport and session lifecycle
• Message Processing - Queue and send messages
• Event Handling - Process SSE events
• Error Management - Classify and respond to errors

Dependencies

MCPGate builds upon three key libraries:

• @modelcontextprotocol/sdk - Core MCP client implementation
• eventsource - Server-Sent Events client for node.js
• node-fetch - Lightweight fetch implementation

These dependencies should be automatically installed when you install mcpgate, so there's no need to install them separately.

Session Persistence Strategy

1. Initial connection establishes a unique session ID
2. On disconnection, attempts to reconnect with the same session ID
3. After multiple failures, falls back to a new session
4. Properly executes handshake sequence to reinitialize connection

Troubleshooting

Common Issues

Logs

All debug information is sent to stderr:

# Filter logs for specific events
mcpgate http://example.com:8000/sse 2>&1 | grep "reconnect"

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

License

This project is licensed under the MIT License - see the LICENSE file for details.

Author

Martin Bukowski