kotlin-sdk/samples/weather-stdio-server

Weather STDIO Server

A minimal MCP server that exposes weather forecast and alert tools using the National Weather Service API over STDIO transport.

Overview

This sample shows how to build a STDIO-based MCP server in Kotlin. It registers two tools that query the weather.gov API — one for weather forecasts by latitude/longitude and one for active alerts by US state. Because it uses STDIO, the server is launched as a subprocess by an MCP client or a desktop application like Claude Desktop.

Prerequisites

• JDK 17+
• Internet access (the server calls the weather.gov API at runtime)

Build & Run

Run the server (it communicates via stdin/stdout):

./gradlew run

MCP Inspector

Build the fat JAR first, then connect with the MCP Inspector:

./gradlew build
npx @modelcontextprotocol/inspector -- java -jar samples/weather-stdio-server/build/libs/weather-stdio-server-0.1.0-all.jar

Claude Desktop integration

Add the following to your Claude Desktop configuration:

{
    "mcpServers": {
        "weather": {
            "command": "java",
            "args": [
                "-jar",
                "/absolute/path/to/samples/weather-stdio-server/build/libs/weather-stdio-server-0.1.0-all.jar"
            ]
        }
    }
}

MCP Capabilities

Tools

Name	Description
get_forecast	Returns weather forecast for a given latitude / longitude using the weather.gov API.
get_alerts	Returns active weather alerts for a two-letter US state code (e.g. CA, NY).

Additional Resources

• MCP Specification
• Kotlin MCP SDK
• National Weather Service API