mcp-hub

MCP Hub

MCP Hub acts as a central coordinator for MCP servers and clients, providing two key interfaces:

1. Management Interface (/api/*): Manage multiple MCP servers through a unified REST API and web UI
2. MCP Server Interface (/mcp): Connect ANY MCP client to access ALL server capabilities through a single endpoint

This dual-interface approach means you can manage servers through the Hub's UI while MCP clients (Claude Desktop, Cline, etc.) only need to connect to one endpoint (localhost:37373/mcp) to access all capabilities. Implements MCP 2025-03-26 specification.

Feature Support

Category	Feature	Support	Notes
Transport
	streamable-http	✅	Primary transport protocol for remote servers
	SSE	✅	Fallback transport for remote servers
	STDIO	✅	For running local servers
Authentication
	OAuth 2.0	✅	With PKCE flow
	Headers	✅	For API keys/tokens
Capabilities
	Tools	✅	List tools
	🔔 Tool List Changed	✅	Real-time updates
	Resources	✅	Full support
	🔔 Resource List Changed	✅	Real-time updates
	Resource Templates	✅	URI templates
	Prompts	✅	Full support
	🔔 Prompts List Changed	✅	Real-time updates
	Roots	❌	Not supported
	Sampling	❌	Not supported
	Completion	❌	Not supported
Marketplace
	Server Discovery	✅	Browse available servers
	Installation	✅	Auto configuration
Real-time
	Status Updates	✅	Server & connection state
	Capability Updates	✅	Automatic refresh
	Event Streaming to clients	✅	SSE-based
	Auto Reconnection	✅	With backoff
Development
	Hot Reload	✅	Auto restart a MCP server on file changes with dev mode
Configuration
	${} Syntax	✅	Environment variables and command execution across all fields
	VS Code Compatibility	✅	Support for servers key, ${env:}, ${input:}, predefined variables
	JSON5 Support	✅	Comments and trailing commas in configuration files

Simplified Client Configuration

Configure all MCP clients with just one endpoint:

{
    "mcpServers" : {
        "Hub": {
            "url" : "http://localhost:37373/mcp"  
        }
    }
}

The Hub automatically:

• Namespaces capabilities to prevent conflicts (e.g., filesystem__search vs database__search)
• Routes requests to the appropriate server
• Updates capabilities in real-time when servers are added/removed
• Handles authentication and connection management

Key Features

• Unified MCP Server Endpoint (/mcp):

  • Single endpoint for ALL MCP clients to connect to
  • Access capabilities from all managed servers through one connection
  • Automatic namespacing prevents conflicts between servers
  • Real-time capability updates when servers change
  • Simplified client configuration - just one endpoint instead of many

• Dynamic Server Management:

  • Start, stop, enable/disable servers on demand
  • Real-time configuration updates with automatic server reconnection
  • Support for local (STDIO) and remote (streamable-http/SSE) MCP servers
  • Health monitoring and automatic recovery
  • OAuth authentication with PKCE flow
  • Header-based token authentication

• 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

• Workspace Management:

  • Track active MCP Hub instances across different working directories
  • Global workspace cache in XDG-compliant state directory
  • Real-time workspace updates via SSE events
  • API endpoints to list and monitor active workspaces

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

Connected services that:

• Provide tools, resources, templates, and prompts
• Support two connectivity modes:
  • Script-based STDIO servers for local operations
  • Remote servers (streamable-http/SSE) with OAuth support
• Implement real-time capability updates
• Support automatic status recovery
• Maintain consistent interface across transport types

Installation

npm install -g mcp-hub

Basic Usage

Start the hub server:

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

# Or with multiple config files (merged in order)
mcp-hub --port 3000 --config ~/.config/mcphub/global.json --config ./.mcphub/project.json

CLI Options

Options:
  --port            Port to run the server on (required)
  --config          Path to config file(s). Can be specified multiple times. Merged in order. (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 JSON configuration files to define managed servers with universal ${} placeholder syntax for environment variables and command execution.

VS Code Configuration Compatibility

MCP Hub provides seamless compatibility with VS Code's .vscode/mcp.json configuration format, enabling you to use the same configuration files across both VS Code and MCP Hub.

Supported Features

Server Configuration Keys

Both mcpServers and servers keys are supported:

{
  "servers": {
    "github": {
      "url": "https://api.githubcopilot.com/mcp/"
    },
    "perplexity": {
      "command": "npx", 
      "args": ["-y", "server-perplexity-ask"],
      "env": {
        "API_KEY": "${env:PERPLEXITY_API_KEY}"
      }
    }
  }
}

Variable Substitution

MCP Hub supports VS Code-style variable substitution:

• Environment Variables: ${env:VARIABLE_NAME} or ${VARIABLE_NAME}
• Workspace Variables: ${workspaceFolder}, ${userHome}, ${pathSeparator}
• Command Execution: ${cmd: command args}

Supported Predefined Variables:

• ${workspaceFolder} - Directory where mcp-hub is running
• ${userHome} - User's home directory
• ${pathSeparator} - OS path separator (/ or )
• ${workspaceFolderBasename} - Just the folder name
• ${cwd} - Alias for workspaceFolder
• ${/} - VS Code shorthand for pathSeparator

VS Code Input Variables

For ${input:} variables used in VS Code configs, use the MCP_HUB_ENV environment variable:

# Set input variables globally
export MCP_HUB_ENV='{"input:api-key":"your-secret-key","input:database-url":"postgresql://..."}'

# Then use in config
{
  "servers": {
    "myserver": {
      "env": {
        "API_KEY": "${input:api-key}"
      }
    }
  }
}

Migration from VS Code

Existing .vscode/mcp.json files work directly with MCP Hub. Simply point MCP Hub to your VS Code configuration:

mcp-hub --config .vscode/mcp.json --port 3000

Multiple Configuration Files

MCP Hub supports loading multiple configuration files that are merged in order. This enables flexible configuration management:

• Global Configuration: System-wide settings (e.g., ~/.config/mcphub/global.json)
• Project Configuration: Project-specific settings (e.g., ./.mcphub/project.json)
• Environment Configuration: Environment-specific overrides

When multiple config files are specified, they are merged with later files overriding earlier ones:

# Global config is loaded first, then project config overrides
mcp-hub --port 3000 --config ~/.config/mcphub/global.json --config ./.mcphub/project.json

Merge Behavior:

• mcpServers sections are merged (server definitions from later files override earlier ones)
• Other top-level properties are completely replaced by later files
• Missing config files are silently skipped

Universal Placeholder Syntax

• ${ENV_VAR} or ${env:ENV_VAR} - Resolves environment variables
• ${cmd: command args} - Executes commands and uses output
• ${workspaceFolder} - Directory where mcp-hub is running
• ${userHome} - User's home directory
• ${pathSeparator} - OS path separator
• ${input:variable-id} - Resolves from MCP_HUB_ENV (VS Code compatibility)
• null or "" - Falls back to process.env

Configuration Examples

Local STDIO Server

{
  "mcpServers": {
    "local-server": {
      "command": "${MCP_BINARY_PATH}/server",
      "args": [
        "--token", "${API_TOKEN}",
        "--database", "${DB_URL}",
        "--secret", "${cmd: op read op://vault/secret}"
      ],
      "env": {
        "API_TOKEN": "${cmd: aws ssm get-parameter --name /app/token --query Parameter.Value --output text}",
        "DB_URL": "postgresql://user:${DB_PASSWORD}@localhost/myapp",
        "DB_PASSWORD": "${cmd: op read op://vault/db/password}",
        "FALLBACK_VAR": null
      },
      "dev": {
        "enabled": true,
        "watch": ["src/**/*.js", "**/*.json"],
        "cwd": "/absolute/path/to/server/directory"
      }
    }
  }
}

Remote Server

{
  "mcpServers": {
    "remote-server": {
      "url": "https://${PRIVATE_DOMAIN}/mcp",
      "headers": {
        "Authorization": "Bearer ${cmd: op read op://vault/api/token}",
        "X-Custom-Header": "${CUSTOM_VALUE}"
      }
    }
  }
}

Configuration Options

MCP Hub supports both STDIO servers and remote servers (streamable-http/SSE). The server type is automatically detected from the configuration. All fields support the universal ${} placeholder syntax.

STDIO Server Options

For running script-based MCP servers locally:

• command: Command to start the MCP server executable (supports ${VARIABLE} and ${cmd: command})
• args: Array of command line arguments (supports ${VARIABLE} and ${cmd: command} placeholders)
• env: Environment variables with placeholder resolution and system fallback
• cwd: The cwd for process spawning the MCP server
• dev: Development mode configuration (optional)
  • enabled: Enable/disable dev mode (default: true)
  • watch: Array of glob patterns to watch for changes (default: ["/*.js", "/.ts", "**/.json"])
  • cwd: Required absolute path to the server's working directory for file watching

Global Environment Variables (MCP_HUB_ENV)

MCP Hub will look for the environment variable MCP_HUB_ENV (a JSON string) in its own process environment. If set, all key-value pairs from this variable will be injected into the environment of every managed MCP server (both stdio and remote). This is useful for passing secrets, tokens, or other shared configuration to all servers without repeating them in each server config.

• Server-specific env fields always override values from MCP_HUB_ENV.
• Example usage:

  MCP_HUB_ENV='{"DBUS_SESSION_BUS_ADDRESS":"/run/user/1000/bus","MY_TOKEN":"abc"}' mcp-hub --port 3000 --config path/to/config.json
  

Remote Server Options

For connecting to remote MCP servers:

• url: Server endpoint URL (supports ${VARIABLE} and ${cmd: command} placeholders)
• headers: Authentication headers (supports ${VARIABLE} and ${cmd: command} placeholders)

Server Type Detection

The server type is determined by:

• STDIO server → Has command field
• Remote server → Has url field

Note: A server configuration cannot mix STDIO and remote server fields.

Placeholder Resolution Order

1. Commands First: ${cmd: command args} are executed first
2. Environment Variables: ${VAR} are resolved from env object, then process.env
3. Fallback: null or "" values fall back to process.env
4. Multi-pass: Dependencies between variables are resolved automatically

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",
  "version": "4.1.1",
  "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"
      }
    ]
  },
  "workspaces": {
    "current": "40123",
    "allActive": {
      "40123": {
        "cwd": "/path/to/project-a",
        "config_files": ["/home/user/.config/mcphub/global.json", "/path/to/project-a/.mcphub/project.json"],
        "pid": 12345,
        "port": 40123,
        "startTime": "2025-01-17T10:00:00.000Z",
        "state": "active",
        "activeConnections": 2,
        "shutdownStartedAt": null,
        "shutdownDelay": null
      }
    }
  }
}

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"
}

Workspace Management

List Active Workspaces

GET /api/workspaces

Response:

{
  "workspaces": {
    "40123": {
      "cwd": "/path/to/project-a",
      "config_files": ["/home/user/.config/mcphub/global.json", "/path/to/project-a/.mcphub/project.json"],
      "pid": 12345,
      "port": 40123,
      "startTime": "2025-01-17T10:00:00.000Z",
      "state": "active",
      "activeConnections": 2,
      "shutdownStartedAt": null,
      "shutdownDelay": null
    },
    "40567": {
      "cwd": "/path/to/project-b",
      "config_files": ["/home/user/.config/mcphub/global.json"],
      "pid": 54321,
      "port": 40567,
      "startTime": "2025-01-17T10:05:00.000Z",
      "state": "shutting_down",
      "activeConnections": 0,
      "shutdownStartedAt": "2025-01-17T10:15:00.000Z",
      "shutdownDelay": 600000
    }
  },
  "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:

{
  "servers": [
    {
      "id": "example-server",
      "name": "Example Server",
      "description": "Description here",
      "author": "example-author",
      "url": "https://github.com/user/repo",
      "category": "search",
      "tags": ["search", "ai"],
      "stars": 100,
      "featured": true,
      "verified": true,
      "lastCommit": 1751257963,
      "updatedAt": 1751265038
    }
  ],
  "timestamp": "2024-02-20T05:55:00.000Z"
}

Get Server Details

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

{
  "mcpId": "example-server"
}

Response:

{
  "server": {
    "id": "example-server",
    "name": "Example Server",
    "description": "Description here",
    "author": "example-author",
    "url": "https://github.com/user/repo",
    "category": "search",
    "tags": ["search", "ai"],
    "installations": [],
    "stars": 100,
    "featured": true,
    "verified": true,
    "lastCommit": 1751257963,
    "updatedAt": 1751265038
  },
  "readmeContent": "# Server Documentation...",
  "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": {},
  "request_options" : {}
}

Access Resource

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

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

Get Prompt

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

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

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:

State	Description
starting	Initial startup, loading configuration
ready	Server is running and ready to handle requests
restarting	Reloading configuration/reconnecting servers
restarted	Configuration reload complete
stopping	Graceful shutdown in progress
stopped	Server has fully stopped
error	Error state (includes error details)

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"
}

7. workspaces_updated - Active workspaces changed

{
  "type": "workspaces_updated",
  "workspaces": {
    "40123": {
      "cwd": "/path/to/project-a",
      "config_files": ["/home/user/.config/mcphub/global.json", "/path/to/project-a/.mcphub/project.json"],
      "pid": 12345,
      "port": 40123,
      "startTime": "2025-01-17T10:00:00.000Z",
      "state": "active",
      "activeConnections": 2,
      "shutdownStartedAt": null,
      "shutdownDelay": null
    }
  },
  "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 following XDG Base Directory Specification:

• XDG compliant: $XDG_STATE_HOME/mcp-hub/logs/mcp-hub.log (typically ~/.local/state/mcp-hub/logs/mcp-hub.log)
• Legacy fallback: ~/.mcp-hub/logs/mcp-hub.log (for backward compatibility)

Example log entry:

{
  "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.

Workspace Cache

MCP Hub maintains a global workspace cache to track active instances across different working directories with real-time lifecycle management:

• Cache Location: $XDG_STATE_HOME/mcp-hub/workspaces.json (typically ~/.local/state/mcp-hub/workspaces.json)
• Purpose: Prevents port conflicts, enables workspace discovery, and provides real-time lifecycle tracking
• Content: Maps port numbers (as keys) to hub process information with detailed lifecycle state
• Cleanup: Automatically removes stale entries when processes are no longer running

Cache Structure

{
  "40123": {
    "cwd": "/path/to/project-a",
    "config_files": ["/home/user/.config/mcphub/global.json", "/path/to/project-a/.mcphub/project.json"],
    "pid": 12345,
    "port": 40123,
    "startTime": "2025-01-17T10:00:00.000Z",
    "state": "active",
    "activeConnections": 2,
    "shutdownStartedAt": null,
    "shutdownDelay": null
  },
  "40567": {
    "cwd": "/path/to/project-b", 
    "config_files": ["/home/user/.config/mcphub/global.json"],
    "pid": 54321,
    "port": 40567,
    "startTime": "2025-01-17T10:05:00.000Z",
    "state": "shutting_down",
    "activeConnections": 0,
    "shutdownStartedAt": "2025-01-17T10:15:00.000Z",
    "shutdownDelay": 600000
  }
}

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

MCP Registry

MCP Hub now uses the MCP Registry system for marketplace functionality. This provides:

• Decentralized Server Discovery: Registry hosted on GitHub Pages for better reliability
• Direct GitHub Integration: README documentation fetched directly from repositories
• Enhanced Metadata: Comprehensive server information including stars, categories, and installation instructions
• Better Caching: Improved cache system with 1-hour TTL for frequent updates
• Fallback Support: Automatic fallback to curl when fetch fails (useful for proxy/VPN environments)

The registry is updated regularly with new servers and improvements to existing entries.

Todo

• Implement custom marketplace rather than depending on mcp-marketplace
• TUI like mcphub.nvim
• Web UI for managing servers

Acknowledgements

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