MCP Hub

A centralized manager for Model Context Protocol (MCP) servers that provides:

• Dynamic MCP server management and monitoring
• REST API for tool execution and resource access
• MCP Server marketplace (using Cline marketplace)
• Real-time server status tracking
• Client connection management
• Process lifecycle handling

Overview

Hub Server vs MCP Servers

• Hub Server (MCP Hub)

  • Central management server that connects to and manages multiple MCP servers
  • Provides unified API endpoints for clients to access MCP server capabilities
  • Handles server lifecycle, health monitoring, and client connections
  • Routes requests between clients and appropriate MCP servers

• MCP Servers

  • Individual servers that provide specific tools and resources
  • Each server has its own capabilities (tools, resources, templates)
  • Connected to and managed by the Hub server
  • Process requests from clients through the Hub

Installation

npm install -g mcp-hub

Basic Usage

Start the hub server:

mcp-hub --port 3000 --config path/to/config.json

CLI Options

Options:
  --port            Port to run the server on (default: 3000)
  --config          Path to config file (required)
  --watch           Watch config file for changes (default: false)
  --shutdown-delay  Delay in milliseconds before shutting down when no clients are connected (default: 0)
  -h, --help       Show help information

The server outputs JSON-formatted status messages on startup and state changes:

{
  "status": "ready",
  "server_id": "mcp-hub",
  "version": "1.0.0",
  "port": 3000,

            
        
            
                  "pid": 12345,
  "servers": [],
  "timestamp": "2024-02-20T05:55:00.000Z"
}

Configuration

MCP Hub uses a JSON configuration file to define managed servers:

{
  "mcpServers": {
    "example-server": {
      "command": "npx",
      "args": ["example-server"],
      "env": {
        "API_KEY": "", // Will use process.env.API_KEY
        "DEBUG": "true", // Will use this value
        "SECRET_TOKEN": null // Will use process.env.SECRET_TOKEN
      },
      "disabled": false
    }
  }
}

Configuration Options

• command: Command to start the MCP server
• args: Array of command line arguments
• env: Environment variables for the server. If a variable is specified with a falsy value (empty string, null, undefined), it will fall back to using the corresponding system environment variable if available.
• disabled: Whether the server is disabled (default: false)

Example Integrations

Neovim Integration

The ravitemer/mcphub.nvim plugin provides seamless integration with Neovim, allowing direct interaction with MCP Hub from your editor:

• Execute MCP tools directly from Neovim
• Access MCP resources within your editing workflow
• Real-time status updates in Neovim
• Auto install mcp servers with marketplace addition

Logging

MCP Hub uses structured JSON logging for all events:

{
  "type": "error",
  "code": "TOOL_ERROR",
  "message": "Failed to execute tool",
  "data": {
    "server": "example-server",
    "tool": "example-tool",
    "error": "Invalid parameters"
  },
  "timestamp": "2024-02-20T05:55:00.000Z"
}

Log levels include:

• info: Normal operational messages
• warn: Warning conditions
• debug: Detailed debug information
• error: Error conditions (includes error code and details)

REST API

Health and Status

Health Check

GET /api/health

Response:

{
  "status": "ok",
  "server_id": "mcp-hub",
  "version": "1.0.0",

            
        
            
                  "activeClients": 2,
  "timestamp": "2024-02-20T05:55:00.000Z",
  "servers": []
}

List MCP Servers

GET /api/servers

Get Server Info

GET /api/servers/:name/info

Refresh Server Capabilities

POST /api/servers/:name/refresh

Response:

{
  "status": "ok",
  "server": {
    "name": "example-server",
    "capabilities": {
      "tools": ["tool1", "tool2"],
      "resources": ["resource1", "resource2"],
      "resourceTemplates": []
    }
  },
  "timestamp": "2024-02-20T05:55:00.000Z"
}

Refresh All Servers

POST /api/refresh

Response:

{
  "status": "ok",
  "servers": [
    {
      "name": "example-server",
      "capabilities": {
        "tools": ["tool1", "tool2"],
        "resources": ["resource1", "resource2"],
        "resourceTemplates": []
      }
    }
  ],
  "timestamp": "2024-02-20T05:55:00.000Z"
}

Start Server

POST /api/servers/:name/start

Response:

{
  "status": "ok",
  "server": {
    "name": "example-server",
    "status": "connected",
    "uptime": 123
  },
  "timestamp": "2024-02-20T05:55:00.000Z"
}

Stop Server

POST /api/servers/:name/stop?disable=true|false

The optional disable query parameter can be set to true to disable the server in the configuration.

Response:

{
  "status": "ok",
  "server": {
    "name": "example-server",
    "status": "disconnected",
    "uptime": 0
  },
  "timestamp": "2024-02-20T05:55:00.000Z"
}

Client Management

Register Client

POST /api/client/register
{
  "clientId": "unique_client_id"
}

Unregister Client

POST /api/client/unregister
{
  "clientId": "unique_client_id"
}

Marketplace Integration

List Available Servers

GET /api/marketplace

Query Parameters:

• search: Filter by name, description, or tags

• category: Filter by category

• tags: Filter by comma-separated tags

            - `sort`: Sort by "newest", "stars", or "name"
  

Response:

{
  "items": [
    {
      "mcpId": "github.com/user/repo/server",
      "name": "Example Server",
      "description": "Description here",
      "category": "search",
      "tags": ["search", "ai"],
      "githubStars": 100,
      "isRecommended": true,
      "createdAt": "2024-02-20T05:55:00.000Z"
    }
  ],
  "timestamp": "2024-02-20T05:55:00.000Z"
}

Get Server Details

POST /api/marketplace/details
Content-Type: application/json

{
  "mcpId": "github.com/user/repo/server"
}

Response:

{
  "server": {
    "mcpId": "github.com/user/repo/server",
    "name": "Example Server",
    "description": "Description here",
    "githubUrl": "https://github.com/user/repo",
    "readmeContent": "# Server Documentation...",
    "llmsInstallationContent": "Installation guide..."
  },
  "timestamp": "2024-02-20T05:55:00.000Z"
}

MCP Server Operations

Execute Tool

POST /api/servers/:name/tools
{
  "tool": "tool_name",
  "arguments": {}
}

Access Resource

POST /api/servers/:name/resources
{
  "uri": "resource://uri"
}

Real-time Updates

The Hub Server provides real-time updates via Server-Sent Events (SSE) at /api/events. Connect to this endpoint to receive real-time updates about server status, client connections, and capability changes.

Event Types

1. server_info - Initial connection information

{
  "server_id": "mcp-hub",
  "version": "1.0.0",
  "status": "connected",
  "pid": 12345,
  "port": 3000,
  "activeClients": 1,
  "timestamp": "2024-02-20T05:55:00.000Z"
}

2. server_ready - Server started and ready

{
  "status": "ready",
  "server_id": "mcp-hub",
  "version": "1.0.0",
  "port": 3000,
  "pid": 12345,
  "servers": [],
  "timestamp": "2024-02-20T05:55:00.000Z"
}

3. client_registered/unregistered - Client connection events

{
  "activeClients": 2,
  "clientId": "client_123",

            
        
            
                  "timestamp": "2024-02-20T05:55:00.000Z"
}

4. tool_list_changed - Server's tools list has changed

{
  "type": "TOOL",
  "server": "example-server",
  "tools": ["tool1", "tool2"],
  "timestamp": "2024-02-20T05:55:00.000Z"
}

5. resource_list_changed - Server's resources list has changed

{
  "type": "RESOURCE",
  "server": "example-server",
  "resources": ["resource1", "resource2"],
  "resourceTemplates": [],
  "timestamp": "2024-02-20T05:55:00.000Z"
}

Error Handling

MCP Hub implements a comprehensive error handling system with custom error classes for different types of errors:

Error Classes

• ConfigError: Configuration-related errors (invalid config, missing fields)
• ConnectionError: Server connection issues (failed connections, transport errors)
• ServerError: Server startup/initialization problems
• ToolError: Tool execution failures
• ResourceError: Resource access issues
• ValidationError: Request validation errors

Each error includes:

• Error code for easy identification
• Detailed error message
• Additional context in the details object
• Stack trace for debugging

Example error structure:

{
  "code": "CONNECTION_ERROR",
  "message": "Failed to communicate with server",
  "details": {
    "server": "example-server",
    "error": "connection timeout"
  },
  "timestamp": "2024-02-20T05:55:00.000Z"
}

Error Categories

1. Configuration Errors

   • Invalid config format
   • Missing required fields
   • Environment variable issues

2. Server Management Errors

   • Connection failures
   • Lost connections
   • Capability fetch issues
   • Server startup problems

3. Request Processing Errors

   • Invalid parameters
   • Server availability
   • Tool execution failures
   • Resource access issues

4. Client Management Errors

   • Registration failures
   • Duplicate registrations
   • Invalid client IDs

Architecture

Hub Server Lifecycle

            ![Hub Lifecycle](public/diagrams/hub-lifecycle.png)

The Hub Server coordinates communication between clients and MCP servers:

1. Starts and connects to configured MCP servers
2. Manages client registrations
3. Routes tool execution and resource requests
4. Handles server monitoring and health checks
5. Performs clean shutdown of all connections

MCP Server Management

The Hub Server actively manages MCP servers through:

1. Configuration-based server initialization
2. Connection and capability discovery
3. Health monitoring and status tracking
4. Automatic reconnection attempts
5. Server state management

Request Handling

All client requests follow a standardized flow:

1. Request validation
2. Server status verification
3. Request routing to appropriate MCP server
4. Response handling and error management

Requirements

• Node.js >= 18.0.0

Todo

• Implement custom marketplace rather than depending on mcp-marketplace

Acknowledgements

• Cline mcp-marketplace - For providing the MCP server marketplace endpoints that power MCP Hub's marketplace integration