elixir_mcp_server

This MCP server is an Elixir implementation of the Model Context Protocol (MCP). It exposes an SSE-based transport for server-sent events and a message endpoint to interact with a set of built-in tools. The available tools include list_files to enumerate directory contents, echo to return a message, and get_weather to fetch weather information using the weather API key provided via WEATHER_API_KEY. To use the server, run it and connect a compliant MCP client (e.g., the MCP Inspector) via the SSE transport to discover and call the tools. The server exposes two endpoints: /sse for streaming tool capabilities and /message for direct tool invocation and responses.

Prerequisites:

• Elixir 1.18 or higher
• Erlang/OTP 27 or higher

Installation steps:

1. Install dependencies

   mix deps.get
   

2. Set required environment variables (example):

   WEATHER_API_KEY="your_weather_api_key_here" mix run --no-halt
   

3. Start the server

   WEATHER_API_KEY="your_weather_api_key_here" mix run --no-halt
   

4. Verify endpoints are accessible:

   • SSE endpoint: http://localhost:4000/sse
   • Message endpoint: http://localhost:4000/message

Note: Ensure your WEATHER_API_KEY is valid for the configured weather service (default is WeatherAPI).

Tips: The WEATHER_API_KEY environment variable is required for the get_weather tool. If you modify or add tools, update handle_initialize/2 accordingly and implement corresponding handle_call_tool/3 clauses. If you experience port or endpoint issues, verify your firewall settings and ensure the application binds to the default port 4000. Common issues include missing dependencies or an invalid API key for the weather service. You can test tools via the MCP Inspector client by selecting SSE as the transport and then listing and invoking available tools. If you need to customize tools, you can extend the tool definitions in the Elixir server code and reload.