met-mcp

# met-mcp

An MCP server for weather forecasts from MET Norway (Yr). Built as a learning project.

Available three ways:

- **npm**: [`met-mcp`](https://www.npmjs.com/package/met-mcp) — run locally over stdio
- **Remote**: `https://met-mcp.met-mcp-worker.workers.dev/mcp` — Streamable HTTP on Cloudflare Workers, add it as a claude.ai connector
- **MCP registry**: [`io.github.trondbjoroy/met-mcp`](https://registry.modelcontextprotocol.io/v0.1/servers?search=io.github.trondbjoroy/met-mcp)

## Tools

- `geocode_location(name, count)` — find coordinates for a place name. Uses the free Open-Meteo geocoder, because MET has no geocoding API.
- `get_forecast(latitude, longitude, hours)` — hourly forecast from MET Locationforecast 2.0. Works worldwide, best in the Nordics.
- `get_nowcast(latitude, longitude)` — radar-based precipitation for the next 2 hours. Nordics only.
- `get_weather_alerts(latitude?, longitude?)` — official Norwegian danger warnings (MetAlerts). Omit coordinates for all of Norway.
- `get_sun_events(latitude, longitude, date, utc_offset)` — sunrise, sunset, and solar noon. Worldwide.
- `get_ocean_forecast(latitude, longitude, hours)` — wave height and sea temperature along the Norwegian coast.
- `find_weather_stations(latitude, longitude, count)` — nearest official weather stations (Frost).
- `get_historical_weather(station_id, from, to, elements)` — daily historical observations from the Frost archive; some stations go back over 100 years.

The two Frost tools need a free client ID from https://frost.met.no/auth/requestCredentials.html, set as the `FROST_CLIENT_ID` env var (or a Cloudflare secret for the worker). The other tools need nothing.

Tool definitions live in `src/tools.ts`, shared between the stdio server and the worker.

## Build and test

```bash
npm install
npm run build
npm test
```

The test spawns the server over stdio and calls both tools against the live APIs.

## Use with Claude Code

```bash
claude mcp add met-weather -- node C:\Users\trond\met-mcp\dist\index.js
```

Then ask Claude: "What is the weather in Bergen tomorrow?"

## MET terms of service

- Send an identifying User-Agent with contact info. Set the `MET_USER_AGENT` env var, e.g. `met-mcp/0.1.0 you@example.com`.
- Send at most 4 decimals in coordinates. The server rounds for you.
- Data license: NLOD / CC BY 4.0. Credit MET Norway when you show the data.

## Remote version

`worker/` holds the Cloudflare Workers deployment: the same two tools served over MCP Streamable HTTP with `createMcpHandler` (MCP SDK v2). Develop with `npm run dev`, ship with `npm run deploy` (both from `worker/`).

## How it works

- `src/index.ts` is the whole server. It speaks MCP over stdio: JSON-RPC on stdin/stdout.
- Each tool declares an input schema with Zod. The MCP client (Claude) reads the schema and validates arguments.
- Tool results are `content` blocks. This server returns JSON as text, trimmed to what an LLM needs — the raw MET response has ~90 timesteps with far more fields.
- Never write to stdout with `console.log`. It corrupts the protocol stream. Log to stderr.