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

Problem	Possible Solution
Connection Refused	Ensure MCP server is running and URL is correct
Authentication Failures	Verify session credentials are valid
Frequent Disconnections	Check network stability and server timeout settings
Delayed Responses	Examine server logs for performance bottlenecks

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

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