MCP Router

The MCP (Model Context Protocol) Router in light-4j allows binding LLM tools to HTTP endpoints, enabling an AI model to interact with your services via the MCP standard. It supports both Server-Sent Events (SSE) for connection establishment and HTTP POST for JSON-RPC messages.

Configuration

The configuration for the MCP Router is defined in mcp-router.yml (or mcp-router.json/yaml). It corresponds to the McpConfig.java class.

Configuration Properties

Property	Type	Default	Description
`enabled`	boolean	`true`	Enable or disable the MCP Router Handler.
`ssePath`	string	`/mcp/sse`	The endpoint path for establishing the MCP Server-Sent Events (SSE) connection.
`messagePath`	string	`/mcp/message`	The endpoint path for sending MCP JSON-RPC messages (POST).
`tools`	list	`null`	A list of tools exposed by this router. Each tool maps to a downstream HTTP service.

Configuration Example (mcp-router.yml)

# Enable MCP Router Handler
enabled: true

# Path for MCP Server-Sent Events (SSE) endpoint
ssePath: /mcp/sse

# Path for MCP JSON-RPC message endpoint
messagePath: /mcp/message

# Define tools exposed by this router
tools:
  - name: getWeather
    description: Get the weather for a location
    host: https://api.weather.com
    path: /v1/current
    method: GET
    # inputSchema is optional; default is type: object

Architecture

The MCP Router implements the MCP HTTP transport specification:

Connection: Clients connect to the ssePath (default /mcp/sse) via GET to establish an SSE session. The server responds with an endpoint event containing the URI for message submission.
Messaging: Clients send JSON-RPC 2.0 messages to the messagePath (default /mcp/message) via POST.
Tool Execution: The router translates tools/call requests into HTTP requests to the configured downstream services (host + path).

Supported Methods

The router supports the following MCP JSON-RPC methods:

initialize: Returns server capabilities (tools list changed notification) and server info.
notifications/initialized: Acknowledgment from the client.
tools/list: Lists all configured tools with their names, descriptions, and input schemas.
tools/call: Executes a specific tool by name. The arguments in the request are passed to the downstream service.

Usage

Example

paths:
  - path: '/mcp/sse'
    method: 'GET'
    exec:
      - mcp-router
  - path: '/mcp/message'
    method: 'POST'
    exec:
      - mcp-router

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