🔌 MCP Bridge (STDIO ↔ SSE)

A lightweight bridge that connects Claude Desktop via STDIO to any MCP-compatible backend using SSE (Server-Sent Events).

This enables Claude to talk to modern MCP servers that expose an HTTP API using /sse and /messages, while Claude only supports STDIO.

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📦 Features

• 🌉 Bridges STDIO and SSE for full protocol compatibility
• 📨 Forwards all JSON-RPC requests to the backend
• 🔁 Relays backend responses and events back to Claude
• 🔧 Fully compatible with the Model Context Protocol (MCP)

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🗂️ Folder Structure

mcp-bridge/
├── cli.ts               # 🧠 Main entry point (runs the bridge logic)
├── package.json         # 📦 Project metadata and dependencies
├── tsconfig.json        # ⚙️ TypeScript config
└── README.md            # 📖 Project documentation

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🚀 Usage

You can run the bridge manually:

npx mcp-bridge http://localhost:4000

Or make the script executable and run it:

chmod +x cli.ts
./cli.ts http://localhost:4000

Alternatively, configure it in your mcpServers:

{
    "mcpServers": {
        "mcp-hub": {
            "command": "npx",
            "args": ["mcp-bridge", "http://localhost:4000"]
        }
    }
}

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⚙️ Requirements

• Node.js v18+ (must support fetch and top-level await)
• TypeScript / tsx if using .ts directly

Your backend must implement:

• GET /sse — SSE endpoint for responses/events
• POST /messages — JSON-RPC POST endpoint for requests

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🧠 How It Works

Claude Desktop
            │
            ▼ (STDIO)
[ MCP Bridge (cli.ts) ]
            │ (SSE + POST)
            ▼
Your MCP Backend (McpServer)

• Claude talks to the bridge over STDIO.
• The bridge opens an SSE connection to your backend's /sse.
• The bridge POSTs Claude's messages to /messages.
• SSE responses are streamed back and passed to Claude via STDOUT.

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🧪 Dev & Debugging

Install dependencies:

npm install

Run in dev mode:

npx tsx cli.ts http://localhost:4000

Enable verbose output:

DEBUG=1 npx tsx cli.ts http://localhost:4000

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🧯 Troubleshooting

• ❌ Permission denied → Run chmod +x cli.ts
• ❌ Unknown file extension .ts → Make sure you're using tsx or ts-node
• ❌ Claude can't connect → Check mcpServers config and stdout/stderr logs

Credits:

boilingdata/mcp-server-and-gw