MCP Proxy Server - Cursor specific fork

A Model Context Protocol (MCP) proxy server that solves three key limitations in Cursor's MCP implementation:

1. The 40-tool limit per server
2. Suboptimal environment variable management
3. Lack of mcp workspace configuration (when different projects require different sets of tools)

This is done with a solution 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
• Filter tools based on allowedTools
• Degrade with visibility into required environment variables

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"
      },
      "allowedTools": ["tool1", "tool2"]
    },
    {
      "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": "npx cursor-mcp-proxy-server",
      "env": {
        "CLIENT_CONFIG_DIRECTORY": "/absolute/path/to/your/project/.cursor",
        "MCP_CONFIG_PATH": "./config.json",
        "CLIENT_CONNECT_RETRIES": "3",
        "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.

Environment Variables

The following environment variables can be configured:

• KEEP_SERVER_OPEN: When set to "1", keeps the SSE server running even if a client disconnects
• CLIENT_CONNECT_RETRIES: Controls the number of retry attempts when connecting to MCP servers (default: 1)
• CLIENT_CONFIG_DIRECTORY: Specifies the directory containing configuration files and environment variables
• MCP_CONFIG_PATH: Specifies the path to the MCP config file relative to the CLIENT_CONFIG_DIRECTORY (default: ./config.json)

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.