MCP Hub

MCP Hub acts as a central coordinator between clients and multiple MCP servers, making it easy to utilize capabilities from multiple servers through a single interface.

Key Features

• Dynamic Server Management:

  • Start, stop, enable/disable servers on demand
  • Real-time configuration updates with automatic server reconnection
  • Support for both local (stdio) and remote (SSE) MCP servers
  • Health monitoring and automatic recovery

• Unified REST API:

  • Execute tools from any connected server
  • Access resources and resource templates
  • Real-time status updates via Server-Sent Events (SSE)
  • Full CRUD operations for server management

• Real-time Events & Monitoring:

  • Live server status and capability updates
  • Client connection tracking
  • Tool and resource list change notifications
  • Structured JSON logging with file output

• Client Connection Management:

  • Simple SSE-based client connections via /api/events
  • Automatic connection cleanup on disconnect
  • Optional auto-shutdown when no clients connected
  • Real-time connection state monitoring

• Process Lifecycle Management:

  • Graceful startup and shutdown handling
  • Proper cleanup of server connections
  • Error recovery and reconnection

Components

Hub Server

The main management server that:

• Maintains connections to multiple MCP servers
• Provides unified API access to server capabilities
• Handles server lifecycle and health monitoring
• Manages SSE client connections and events
• Processes configuration updates and server reconnection

MCP Servers

Individual servers that:

• Provide specific tools and resources
• Can be local processes (STDIO) or remote endpoints (SSE)
• Have their own set of capabilities (tools, resources, templates)
• Are dynamically managed by 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 (required)
  --config          Path to config file (required)
  --watch           Watch config file for changes, only updates affected servers (default: false)
  --auto-shutdown   Whether to automatically shutdown when no clients are connected (default: false)
  --shutdown-delay  Delay in milliseconds before shutting down when auto-shutdown is enabled (default: 0)
  -h, --help       Show help information

Configuration

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

{
  "mcpServers": {
    "stdio-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
    },
      "sse-server": {
        "url": "https://api.example.com/mcp",
        "headers": {
          "Authorization": "Bearer token",
          "Content-Type": "application/json"
        },
        "disabled": false
      }
  }
}

Configuration Options

MCP Hub supports two types of servers: STDIO (local) and SSE (remote). The server type is automatically determined based on the configuration fields provided.

STDIO Server Options

• command: Command to start the local 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)

SSE Server Options

• url: The URL of the remote SSE server endpoint
• headers: Optional HTTP headers for the SSE connection (e.g., for authentication)
• disabled: Whether the server is disabled (default: false)

Server Type Detection

The server type (STDIO or SSE) is automatically determined based on the presence of specific fields:

• If command is present → STDIO server
• If url is present → SSE server

Note: A server configuration cannot mix STDIO and SSE fields - it must be one type or the other.

Nix

Nixpkgs install

coming...

Flake install

Just add it to your NixOS flake.nix or home-manager:

inputs = {
  mcp-hub.url = "github:ravitemer/mcp-hub";
  ...
}

To integrate mcp-hub to your NixOS/Home Manager configuration, add the following to your environment.systemPackages or home.packages respectively:

inputs.mcp-hub.packages."${system}".default

Usage without install

If you want to use mcphub.nvim without having mcp-hub server in your PATH you can link the server under the hood adding the mcp-hub nix store path to the cmd command in the plugin config like

Nixvim example:

{ mcphub-nvim, mcp-hub, ... }:
{
  extraPlugins = [mcphub-nvim];
  extraConfigLua = ''
    require("mcphub").setup({
        port = 3000,
        config = vim.fn.expand("~/mcp-hub/mcp-servers.json"),
        cmd = "${mcp-hub}/bin/mcp-hub"
    })
  '';
}

# where
{
  # For nixpkgs (not available yet)
  mcp-hub = pkgs.mcp-hub;

  # For flakes
  mcp-hub = inputs.mcp-hub.packages."${system}".default;
}

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

REST API

Health and Status

Health Check

GET /api/health

The health endpoint provides comprehensive status information including:

• Current hub state (starting, ready, restarting, restarted, stopping, stopped, error)
• Connected server statuses and capabilities
• Active SSE connection details
• Detailed connection metrics
• Error state details if applicable

Response:

{
  "status": "ok",
  "state": "ready",
  "server_id": "mcp-hub",
  "activeClients": 2,
  "timestamp": "2024-02-20T05:55:00.000Z",
  "servers": [],
  "connections": {
    "totalConnections": 2,
    "connections": [
      {
        "id": "client-uuid",
        "state": "connected",
        "connectedAt": "2024-02-20T05:50:00.000Z",
        "lastEventAt": "2024-02-20T05:55:00.000Z"
      }
    ]
  }
}

List MCP Servers

GET /api/servers

Get Server Info

POST /api/servers/info
Content-Type: application/json

{
  "server_name": "example-server"
}

Refresh Server Capabilities

POST /api/servers/refresh
Content-Type: application/json

{
  "server_name": "example-server"
}

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/start
Content-Type: application/json

{
  "server_name": "example-server"
}

Response:

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

Stop Server

POST /api/servers/stop?disable=true|false
Content-Type: application/json

{
  "server_name": "example-server"
}

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"
}

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/tools
Content-Type: application/json

{
  "server_name": "example-server",
  "tool": "tool_name",
  "arguments": {}
}

Access Resource

POST /api/servers/resources
Content-Type: application/json

{
  "server_name": "example-server",
  "uri": "resource://uri"
}

Get Prompt

POST /api/servers/prompts
Content-Type: application/json

{
  "server_name": "example-server",
  "prompt": "prompt_name",
  "arguments": {}
}

Response:

{
  "result": {
    "messages": [
      {
        "role": "assistant",
        "content": {
          "type": "text",
          "text": "Text response example"
        }
      },
      {
        "role": "assistant",
        "content": {
          "type": "image",
          "data": "base64_encoded_image_data",
          "mimeType": "image/png"
        }
      }
    ]
  },
  "timestamp": "2024-02-20T05:55:00.000Z"
}

Restart Hub

POST /api/restart

Reloads the configuration file and restarts all MCP servers.

Response:

{
  "status": "ok",
  "timestamp": "2024-02-20T05:55:00.000Z"
}

Real-time Events System

MCP Hub implements a comprehensive real-time events system using Server-Sent Events (SSE) at /api/events. This endpoint provides live updates about server status, configuration changes, capability updates, and more.

Hub States

The hub server transitions through several states during its lifecycle:

You can monitor these states through the /health endpoint or SSE events.

Event Types

MCP Hub emits several types of events:

Core Events

1. heartbeat - Periodic connection health check

{
  "connections": 2,
  "timestamp": "2024-02-20T05:55:00.000Z"
}

2. hub_state - Hub server state changes

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

3. log - Server log messages

{
  "type": "info",
  "message": "Server started",
  "data": {},
  "timestamp": "2024-02-20T05:55:00.000Z"
}

Subscription Events

1. config_changed - Configuration file changes detected

{
  "type": "config_changed",
  "newConfig": {},
  "isSignificant": true,
  "timestamp": "2024-02-20T05:55:00.000Z"
}

2. servers_updating - Server updates in progress

{
  "type": "servers_updating",
  "changes": {
    "added": ["server1"],
    "removed": [],
    "modified": ["server2"],
    "unchanged": ["server3"]
  },
  "timestamp": "2024-02-20T05:55:00.000Z"
}

3. servers_updated - Server updates completed

{
  "type": "servers_updated",
  "changes": {
    "added": ["server1"],
    "removed": [],
    "modified": ["server2"],
    "unchanged": ["server3"]
  },
  "timestamp": "2024-02-20T05:55:00.000Z"
}

4. tool_list_changed - Server's tools list updated

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

5. resource_list_changed - Server's resources/templates updated

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

6. prompt_list_changed - Server's prompts list updated

{
  "type": "prompt_list_changed",
  "server": "example-server",
  "prompts": ["prompt1", "prompt2"],
  "timestamp": "2024-02-20T05:55:00.000Z"
}

Connection Management

• Each SSE connection is assigned a unique ID
• Connections are automatically cleaned up on client disconnect
• Connection statistics available via /health endpoint
• Optional auto-shutdown when no clients are connected

Logging

MCP Hub uses structured JSON logging for all events. Logs are written to both console and file at ~/.mcp-hub/logs/mcp-hub.log:

{
  "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 (includes configuration changes)
• error: Error conditions (includes error code and stack trace)

Logs are rotated daily and kept for 30 days by default.

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"
}

Architecture

Hub Server Lifecycle

sequenceDiagram
    participant C as Client
    participant H as Hub Server
    participant M1 as MCP Server 1
    participant M2 as MCP Server 2

    Note over H: Server Start (state: starting)
    activate H
    
    Note over H: Config Loading
    H->>H: Load & Validate Config
    H->>H: Watch Config File
    H->>H: Initialize SSE Manager
    
    Note over H: Server Connections (state: ready)
    H->>+M1: Connect
    M1-->>-H: Connected + Capabilities
    H->>+M2: Connect
    M2-->>-H: Connected + Capabilities
    H-->>C: hub_state (ready)

    Note over C,H: Client Setup
    C->>H: Connect to /api/events (SSE)
    H-->>C: connection_opened
    
    Note over C,H: Client Operations
    C->>H: Execute Tool (HTTP)
    H->>M1: Execute Tool
    M1-->>H: Tool Result
    H-->>C: HTTP Response
    
    Note over H,C: Real-time Updates
    H->>H: Detect Config Change
    H-->>C: servers_updating (SSE)
    H->>M1: Reconnect with New Config
    M1-->>H: Updated Capabilities
    H-->>C: servers_updated (SSE)

    Note over H,C: Server Events
    M2->>H: Tool List Changed
    H-->>C: tool_list_changed (SSE)
    
    Note over H: Shutdown Process
    Note over C,H: Client Disconnects
    H-->>C: hub_state (stopping) (SSE)
    H->>M1: Disconnect
    H->>M2: Disconnect
    H-->>C: hub_state (stopped) (SSE)
    deactivate H

The Hub Server coordinates communication between clients and MCP servers:

1. Starts and connects to configured MCP servers
2. Handles SSE client connections and events
3. Routes tool and resource requests to appropriate servers
4. Monitors server health and maintains capabilities
5. Manages graceful startup/shutdown processes

MCP Server Management

flowchart TB
    A[Hub Server Start] --> B{Config Available?}
    B -->|Yes| C[Load Server Configs]
    B -->|No| D[Use Default Settings]
    
    C --> E[Initialize Connections]
    D --> E
    
    E --> F{For Each MCP Server}
    F -->|Enabled| G[Attempt Connection]
    F -->|Disabled| H[Skip Server]
    
    G --> I{Connection Status}
    I -->|Success| J[Fetch Capabilities]
    I -->|Failure| K[Log Error]
    
    J --> L[Store Server Info]
    K --> M[Mark Server Unavailable]
    
    L --> N[Monitor Health]
    M --> N
    
    N --> O{Health Check}
    O -->|Healthy| P[Update Capabilities]
    O -->|Unhealthy| Q[Attempt Reconnect]
    
    Q -->|Success| P
    Q -->|Failure| R[Update Status]
    
    P --> N
    R --> N

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

sequenceDiagram
    participant C as Client
    participant H as Hub Server
    participant M as MCP Server
    
    Note over C,H: Tool Execution
    C->>H: POST /api/servers/tools (HTTP)
    H->>H: Validate Request & Server
    
    alt Server Not Connected
        H-->>C: 503 Server Unavailable (HTTP)
    else Server Connected
        H->>M: Execute Tool
        
        alt Success
            M-->>H: Tool Result
            H-->>C: Result Response (HTTP)
        else Error
            M-->>H: Error Details
            H-->>C: Error Response (HTTP)
            H-->>C: log (SSE Event)
        end
    end
    
    Note over C,H: Resource Access
    C->>H: POST /api/servers/resources (HTTP)
    H->>H: Validate URI & Template
    
    alt Invalid Resource
        H-->>C: 404 Not Found (HTTP)
    else Server Not Connected
        H-->>C: 503 Unavailable (HTTP)
    else Valid Request
        H->>M: Request Resource
        
        alt Success
            M-->>H: Resource Data
            H-->>C: Resource Content (HTTP)
        else Error
            M-->>H: Error Details
            H-->>C: Error Response (HTTP)
            H-->>C: log (SSE Event)
        end
    end
    
    Note over C,H: Prompt Execution
    C->>H: POST /api/servers/prompts (HTTP)
    H->>H: Validate Prompt & Args
    
    alt Invalid Prompt
        H-->>C: 404 Not Found (HTTP)
    else Server Not Connected
        H-->>C: 503 Unavailable (HTTP)
    else Valid Request
        H->>M: Execute Prompt
        
        alt Success
            M-->>H: Messages Array
            H-->>C: Messages Response (HTTP)
        else Error
            M-->>H: Error Details
            H-->>C: Error Response (HTTP)
            H-->>C: log (SSE Event)
        end
    end

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