MCP SSE Proxy

A Model Context Protocol (MCP) server that acts as a proxy, bridging STDIO-based MCP clients with SSE (Server-Sent Events) based MCP servers. This enables MCP clients that only support STDIO transport to connect to remote MCP servers that use SSE transport.

Overview

The MCP SSE Proxy creates a bridge between two different MCP transport protocols:

• STDIO Transport: Used by local MCP clients (like Claude Desktop)

• SSE Transport: Used by remote MCP servers accessible via HTTP/HTTPS

This proxy allows you to use remote MCP servers that expose SSE endpoints from applications that only support STDIO-based MCP connections.

Features

• Full MCP Protocol Support: Proxies all MCP capabilities including:

  • Tools (listing and calling)

  • Resources (listing and reading)

  • Resource Templates (listing)

  • Prompts (listing and getting)

• Authentication Support: Optional API key authentication for SSE endpoints

• Error Handling: Comprehensive error handling with detailed logging

• Graceful Shutdown: Proper cleanup on process termination

• Configurable: Flexible configuration via command line arguments or environment variables

Installation

Prerequisites

• Node.js >= 18.0.0

• npm or yarn

Setup

1. Clone or download this repository

2. Install dependencies:

Usage

Command Line Arguments

Parameters:

• SERVER_NAME: Display name for the MCP server

• SSE_URL: URL of the remote SSE MCP server endpoint

• API_KEY: (Optional) API key for authentication

Example:

Environment Variables

Alternatively, you can use environment variables:

Configuration

MCP Client Configuration

To use this proxy with an MCP client like Claude Desktop, add the following to your MCP configuration:

Authentication

The proxy supports Bearer token authentication. When an API key is provided, it will be sent as:

• Authorization: Bearer <API_KEY> header in HTTP requests

• Authentication headers for EventSource connections

Creating a Desktop Extension (.dxt)

This MCP proxy can be packaged as a Desktop Extension for easy one-click installation in Claude Desktop and other MCP-enabled applications.

For the complete guide, see: Desktop Extensions: One-click MCP server installation for Claude Desktop

Prerequisites

Install dependencies

Install the DXT CLI tool:

Steps to Create DXT File

1. Initialize DXT configuration (if needed):

   dxt init

   Note: This project already includes a manifest.json file, so initialization may not be necessary.

2. Validate the manifest:

   dxt validate

3. Package the extension:

   dxt pack

4. Test the extension:

   • The command will generate a .dxt file

   • Drag the .dxt file into Claude Desktop's Settings window

   • Click "Install" to test the extension

Quick Installation (Alternative)

If you don't want to build the extension yourself, you can directly drag and drop the pre-built mcp-proxy-node.dxt file into Claude Desktop's Settings window for immediate installation.

Screenshots

The MCP SSE Proxy extension as it appears in Claude Desktop after installation. Users can easily configure the server name, SSE URL, and API key through the intuitive interface.

Technical Details

Architecture

The proxy consists of two main components:

1. MCP Server: Accepts STDIO connections from local MCP clients

2. MCP Client: Connects to remote SSE MCP servers

Transport Protocols

• Input: STDIO transport (standard input/output)

• Output: SSE transport (Server-Sent Events over HTTP/HTTPS)

Error Handling

The proxy includes comprehensive error handling:

• Connection failures to remote SSE servers

• Invalid URL formats

• Authentication errors

• Request/response parsing errors

• Graceful degradation when remote capabilities are unavailable

Logging

Detailed logging is provided via console.error() for debugging:

• Connection status

• Request/response details

• Error information with stack traces

• Performance metrics

API Reference

MCPSSEProxy Class

Constructor

• sseUrl (string): URL of the SSE MCP server

• apiKey (string, optional): API key for authentication

• serverName (string): Display name for the proxy server

Methods

• initialize(): Initialize client and server connections

• run(): Start the proxy server

• close(): Gracefully shutdown the proxy

• setupProxyHandlers(): Configure request handlers

Development

Project Structure

Dependencies

• @modelcontextprotocol/sdk: Official MCP SDK for Node.js

Contributing

1. Fork the repository

2. Create a feature branch

3. Make your changes

4. Test thoroughly

5. Submit a pull request

Troubleshooting

Common Issues

1. Connection Refused

   • Verify the SSE URL is correct and accessible

   • Check if the remote server is running

   • Ensure firewall/network settings allow connections

2. Authentication Errors

   • Verify the API key is correct

   • Check if the remote server expects authentication

   • Ensure the API key format matches server expectations

3. No Tools/Resources Available

   • Check if the remote server actually provides tools/resources

   • Verify the remote server is responding correctly

   • Check proxy logs for error messages

4. Performance Issues

   • Monitor network latency to the remote server

   • Check for rate limiting on the remote server

   • Consider connection pooling for high-frequency usage

Debugging

Enable detailed logging by examining the console output. The proxy logs:

• Connection attempts and results

• Request/response details

• Error messages with stack traces

• Performance timing

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License

MIT License - see LICENSE file for details

Support

For issues and questions:

• Check the troubleshooting section above

• Review the console logs for error details

• Ensure your Node.js version meets requirements (>= 18.0.0)

• Verify the remote SSE server is compatible with MCP protocol

Compatibility

• Node.js: >= 18.0.0

• MCP Protocol: Compatible with MCP SDK v1.13.2+

• Platforms: macOS, Windows, Linux

• Claude Desktop: >= 0.10.0

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