mcpd-proxy

An MCP (Model Context Protocol) server that acts as a proxy between IDEs and the mcpd daemon, exposing all mcpd-managed MCP servers through a unified interface.

Overview

┌─────────────┐   STDIO/JSON-RPC    ┌──────────────┐    HTTP/REST     ┌──────────┐
│  IDE/Editor │ ◄─────────────────► │  mcpd-proxy  │ ◄───────────────►│   mcpd   │
│ (VS Code,   │     MCP Protocol    │  MCP Server  │   Uses mcpd SDK  │  daemon  │
│  Cursor)    │                     │              │                  │          │
└─────────────┘                     └──────────────┘                  └──────────┘

mcpd-proxy aggregates tools, resources, and prompts from multiple MCP servers managed by mcpd into a single MCP interface, making it easy for IDEs to access all capabilities without managing individual server connections.

Features

• Unified Interface: Single MCP server exposing all mcpd-managed capabilities
• Tool Aggregation: Tools from all servers with server__tool naming convention
• Resource Aggregation: Resources from all servers with server__resource naming and mcpd:// URIs
• Prompt Aggregation: Prompts from all servers with server__prompt naming convention
• Efficient Caching: Leverages SDK caching for health checks and tool schemas
• Zero Configuration: Works out of the box with sensible defaults
• TypeScript: Built with TypeScript for type safety

Prerequisites

• Node.js 22.10.0 or higher (latest 22.x recommended)
• mcpd daemon running and accessible
• mcpd SDK (automatically installed as a dependency)

Installation

From npm (Recommended)

# Global installation
npm install -g @mozilla-ai/mcpd-proxy

# Or use directly with npx
npx @mozilla-ai/mcpd-proxy

From Source

# Clone the repository
git clone https://github.com/mozilla-ai/mcpd-proxy.git
cd mcpd-proxy

# Install dependencies
npm install

# Build the project
npm run build

Configuration

mcpd-proxy is configured via environment variables:

| Variable | Description | Default | | -------------- | ------------------------------------------ | ----------------------- | | MCPD_ADDR | mcpd daemon address | http://localhost:8090 | | MCPD_API_KEY | Optional API key for mcpd authentication | (not set) |

Usage

Running Directly

# Using npm package (recommended)
npx @mozilla-ai/mcpd-proxy

# With custom mcpd address
MCPD_ADDR=http://localhost:8090 npx @mozilla-ai/mcpd-proxy

# With API key
MCPD_ADDR=http://localhost:8090 MCPD_API_KEY=your-key npx @mozilla-ai/mcpd-proxy

# From source build
node dist/index.mjs

# From source with custom address
MCPD_ADDR=http://localhost:8090 node dist/index.mjs

VS Code Setup

Add to your VS Code MCP settings file (location varies by platform):

{
  "servers": {
    "mcpd": {
      "type": "stdio",
      "command": "npx",
      "args": ["@mozilla-ai/mcpd-proxy"],
      "env": {
        "MCPD_ADDR": "http://localhost:8090"
      }
    }
  }
}

Or if building from source:

{
  "servers": {
    "mcpd": {
      "type": "stdio",
      "command": "node",
      "args": ["<path-to-mcpd-proxy>/dist/index.mjs"],
      "env": {
        "MCPD_ADDR": "http://localhost:8090"
      }
    }
  }
}

Replace <path-to-mcpd-proxy> with the absolute path to your installation.

Reload VS Code: Cmd+Shift+P → "Developer: Reload Window"

Verify the connection in the MCP panel to see available tools.

Cursor Setup

Create or edit .cursor/mcp.json in your project directory, or ~/.cursor/mcp.json for global configuration:

{
  "mcpServers": {
    "mcpd": {
      "command": "npx",
      "args": ["@mozilla-ai/mcpd-proxy"],
      "env": {
        "MCPD_ADDR": "http://localhost:8090"
      }
    }
  }
}

Or if building from source:

{
  "mcpServers": {
    "mcpd": {
      "command": "node",
      "args": ["<path-to-mcpd-proxy>/dist/index.mjs"],
      "env": {
        "MCPD_ADDR": "http://localhost:8090"
      }
    }
  }
}

Replace <path-to-mcpd-proxy> with the absolute path to your installation, or use ${workspaceFolder} for relative paths.

Reload Cursor to apply the configuration.

See examples/ folder for configuration examples.

Development

Project Structure

mcpd-proxy/
├── src/
│   ├── index.ts               # CLI entry point
│   ├── server.ts              # MCP server implementation
│   ├── config.ts              # Configuration loader
│   └── apiPaths.ts            # API endpoint constants
├── tests/
│   └── unit/                  # Unit test files
│       ├── aggregation.test.ts
│       ├── apiPaths.test.ts
│       ├── config.test.ts
│       ├── parsers.test.ts
│       └── server.test.ts
├── .github/
│   └── workflows/             # GitHub Actions workflows
│       ├── tests.yaml
│       ├── lint.yaml
│       └── release.yaml
├── examples/
│   ├── vscode-config.json     # VS Code configuration example
│   └── cursor-config.json     # Cursor configuration example
├── dist/                      # Build output (gitignored)
├── package.json               # npm package configuration
├── package-lock.json          # npm dependency lock file
├── tsconfig.json              # TypeScript compiler configuration
├── tsconfig.test.json         # TypeScript test configuration
├── vitest.config.ts           # Vitest test configuration
├── vite.config.mts            # Vite build configuration
├── eslint.config.mts          # ESLint configuration
├── .prettierignore            # Prettier ignore patterns
├── .gitignore                 # Git ignore patterns
└── README.md                  # This file

Development Workflow

# Install dependencies
npm install

# Build once
npm run build

# Watch mode (auto-rebuild on changes)
npm run dev

# Run tests
npm test

# Run tests in watch mode
npm run test:watch

# Type check without building
npm run typecheck

# Lint code
npm run lint

# Format code
npm run format

Manual Testing

Test the MCP protocol directly using JSON-RPC over stdio:

# Test initialize
echo '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2024-11-05","capabilities":{},"clientInfo":{"name":"test","version":"1.0.0"}}}' | node dist/index.mjs

# Test list tools
echo '{"jsonrpc":"2.0","id":2,"method":"tools/list","params":{}}' | node dist/index.mjs

Naming Conventions

Tools

Tools are exposed with the format: {server}__{tool_name}

Examples:

• time__get_current_time - get_current_time tool from time server
• github__create_issue - create_issue tool from github server
• fetch__get_url - get_url tool from fetch server

This naming convention prevents tool name collisions between servers and makes it clear which server provides each tool.

Resources

Resources use a custom URI scheme: mcpd://{server}/{resource_uri}

Examples:

• mcpd://filesystem/documents/file.txt
• mcpd://database/users/123

Prompts

Prompts follow the same naming convention as tools: {server}__{prompt_name}

Architecture

Singleton McpdClient

mcpd-proxy creates a single instance of McpdClient at startup and reuses it for all requests. This is essential for:

• Caching: Health check cache (10s TTL) and tool schema cache (60s TTL)
• Performance: Avoids creating new HTTP connections for each request
• Efficiency: Reduces load on mcpd daemon

const mcpdClient = new McpdClient({
  apiEndpoint: config.mcpdAddr,
  apiKey: config.mcpdApiKey,
  healthCacheTtl: 10,
});

MCP Protocol Handlers

The proxy implements the following MCP protocol handlers:

• initialize - Handshake with IDE, declares capabilities
• tools/list - Aggregates tools from all mcpd servers
• tools/call - Parses tool name and forwards to mcpd
• resources/list - Aggregates resources from all servers
• resources/read - Forwards resource read requests to mcpd
• prompts/list - Aggregates prompts from all servers
• prompts/get - Forwards prompt requests to mcpd
• ping - Health check endpoint

Troubleshooting

Cannot connect to mcpd daemon

Cause: mcpd daemon is not running or not accessible

Solution:

1. Verify mcpd is running: curl http://localhost:8090/api/v1/servers
2. Check MCPD_ADDR environment variable is correct
3. Ensure no firewall blocking the connection

Server not found

Cause: Requested server doesn't exist in mcpd

Solution:

1. List available servers: curl http://localhost:8090/api/v1/servers
2. Check server is configured in mcpd
3. Verify server is healthy: curl http://localhost:8090/api/v1/health/servers/<server-name>

VS Code not showing tools

Cause: VS Code may not have recognized the MCP server

Solution:

1. Check VS Code developer console for errors (Help → Toggle Developer Tools)
2. Verify the path to dist/index.mjs is correct and absolute (if building from source)
3. Reload VS Code: Cmd+Shift+P → "Developer: Reload Window"
4. Check mcpd daemon is running and accessible

Tools listed but execution fails

Cause: Server may be unhealthy or tool doesn't exist

Solution:

1. Check server health via mcpd API
2. Verify tool exists on the server
3. Check mcpd logs for errors

Future Enhancements

• Dynamic tool list updates (notifications/tools/list_changed)
• Server filtering via MCPD_SERVERS environment variable
• Improved unhealthy server handling

Related Projects

• mcpd - The MCP daemon this proxy connects to
• mcpd-sdk-javascript - TypeScript SDK for mcpd
• mcpd-sdk-python - Python SDK for mcpd

License

Apache-2.0

Contributing

See the main mcpd repository for contribution guidelines.