MCP Proxy Server

MCP Proxy Server

An MCP proxy server that aggregates and serves multiple MCP resource servers through a single interface. This server acts as a central hub that can:

• Connect to and manage multiple MCP resource servers
• Expose their combined capabilities through a unified interface
• Handle routing of requests to appropriate backend servers
• Aggregate responses from multiple sources

Features

Resource Management

• Discover and connect to multiple MCP resource servers
• Aggregate resources from all connected servers
• Maintain consistent URI schemes across servers
• Handle resource routing and resolution

Tool Aggregation

• Expose tools from all connected servers
• Route tool calls to appropriate backend servers
• Maintain tool state and handle responses

Prompt Handling

• Aggregate prompts from all connected servers
• Route prompt requests to appropriate backends
• Handle multi-server prompt responses

Configuration

The server requires a JSON configuration file that specifies the MCP servers to connect to. Copy the example config and modify it for your needs:

cp config.example.json config.json

Example config structure:

{
  "servers": [
    {
      "name": "Server 1",
      "transport": {
        "command": "/path/to/server1/build/index.js"
      }
    },
    {
      "name": "Server 2",
      "transport": {
        "command": "server2-command",
        "args": ["--option1", "value1"],
        "env": ["SECRET_API_KEY"]
      }
    },
    {
      "name": "Example Server 3",
      "transport": {
        "type": "sse",
        "url": "http://localhost:8080/sse"
      }
    }
  ]
}

The config file must be provided when running the server:

MCP_CONFIG_PATH=./config.json mcp-proxy-server

Development

Install dependencies:

npm install

Build the server:

npm run build

For development with auto-rebuild:

npm run watch

For development with continuous run:

# Stdio
npm run dev
# SSE
npm run dev:sse

Installation

To use with Claude Desktop, add the server config:

On MacOS: ~/Library/Application Support/Claude/claude_desktop_config.json On Windows: %APPDATA%/Claude/claude_desktop_config.json

{
  "mcpServers": {
    "mcp-proxy": {
      "command": "/path/to/mcp-proxy-server/build/index.js",
      "env": {
        "MCP_CONFIG_PATH": "/absolute/path/to/your/config.json",
        "KEEP_SERVER_OPEN": "1"
      }
    }
  }
}

• KEEP_SERVER_OPEN will keep the SSE running even if a client disconnects. Useful when multiple clients connects to the MCP proxy.

Debugging

Since MCP servers communicate over stdio, debugging can be challenging. We recommend using the MCP Inspector, which is available as a package script:

npm run inspector

The Inspector will provide a URL to access debugging tools in your browser.