mcp-weather-service

An MCP server that gives an AI assistant live weather data. It speaks JSON-RPC over stdio — there is no HTTP port and nothing to open in a browser. An MCP client (Claude Desktop, Claude Code, the MCP Inspector) spawns the process and talks to it over the pipe.

Tools

get_current_weather and get_forecast accept either a location name ("Tokyo", "Paris,FR") or explicit latitude/longitude, plus an optional units of metric (default) or imperial.

get_alerts is US-only and needs no API key — the NWS API is public. Alerts come from NWS rather than OpenWeather because OpenWeather only exposes them on the paid One Call 3.0 plan.

Prerequisites

• Node.js 18+ (uses the global fetch)

• A free OpenWeather API key

Setup

npm install
npm run build

build/ is gitignored, so a fresh clone must run npm run build before the server will start.

Configuration

The key is read from the OPENWEATHER_API_KEY environment variable and is never hardcoded.

Note that the MCP SDK does not pass your shell environment to the server it spawns — on Windows it copies only an allowlist (PATH, APPDATA, TEMP, …). Setting the variable in your terminal is therefore not enough for MCP clients; it must be handed over explicitly via an env block or the -e flag.

Copy the template and fill in your key:

cp mcp.example.json mcp.json

mcp.json is gitignored — keep your real key out of version control.

Running it

MCP Inspector

npm run inspect

Serves a web UI at http://localhost:6274. Open the URL including the MCP_INSPECTOR_API_TOKEN query parameter it prints; the token changes on every launch.

--config replaces the server command rather than supplementing it — passing both a config file and node build/index.js is an error.

For a one-shot check with no browser:

npx @modelcontextprotocol/inspector --cli --config mcp.json --server weather \
  --method tools/call --tool-name get_current_weather --tool-arg location=Tokyo

In --cli mode the server command must come before any flags. Leading with -e yields a misleading No servers found in config file.

Claude Desktop

Add the server to claude_desktop_config.json:

• Windows — %APPDATA%\Claude\claude_desktop_config.json

• macOS — ~/Library/Application Support/Claude/claude_desktop_config.json

{
  "mcpServers": {
    "weather": {
      "command": "node",
      "args": ["/absolute/path/to/weather-mcp/build/index.js"],
      "env": { "OPENWEATHER_API_KEY": "your-key-here" }
    }
  }
}

Use an absolute path for args. On Windows, prefer an absolute path to node.exe (e.g. C:\\Program Files\\nodejs\\node.exe) — Claude Desktop launches outside your shell, and a bare node failing to resolve is the most common reason the server never appears.

Restart Claude Desktop fully afterward (File → Exit — it stays in the tray, so closing the window does not reload the config), then ask "What's the weather in Tokyo?"

Server logs land in %APPDATA%\Claude\logs\mcp-server-weather.log.

Claude Code

claude mcp add weather -e OPENWEATHER_API_KEY=your-key-here -- node /absolute/path/to/weather-mcp/build/index.js

Scripts

There is no watch mode: MCP clients execute build/index.js, so run npm run build after every change to src/ or you will keep testing stale code.

Project layout

src/index.ts        server, tool definitions, API clients
build/index.js      compiled output (gitignored)
mcp.example.json    config template — copy to mcp.json

License

ISC