mcp-norwegian-weather

Instructions

Implementation Reference

• src/index.js:108-136 (registration)

  Tool registration: The current_weather tool is registered with the MCP server using server.tool() with its name, description, input schema, and handler function.

  server.tool(
    "current_weather",
    "Get current weather for a location in Norway using MET Norway (yr.no).",
    { location: z.string().describe("Norwegian city name or lat,lon coordinates") },
    async ({ location }) => {
      try {
        const loc = await getLocation(location);
        const data = await fetchForecast(loc.lat, loc.lon);
        const now = data.properties.timeseries[0];
        const inst = now.data.instant.details;
        const symbol = now.data.next_1_hours?.summary?.symbol_code || now.data.next_6_hours?.summary?.symbol_code || "";
        const precip1h = now.data.next_1_hours?.details?.precipitation_amount;
        const lines = [
          `## ${loc.name} — Current Weather`,
          `**Conditions:** ${symbolToText(symbol)}`,
          `**Temperature:** ${inst.air_temperature}°C`,
          `**Humidity:** ${inst.relative_humidity}%`,
          `**Wind:** ${inst.wind_speed} m/s from ${inst.wind_from_direction}° (gusts ${inst.wind_speed_of_gust ?? "N/A"} m/s)`,
          `**Pressure:** ${inst.air_pressure_at_sea_level} hPa`,
          `**Cloud cover:** ${inst.cloud_area_fraction}%`,
          precip1h != null ? `**Precipitation (next hour):** ${precip1h} mm` : null,
          `\n*MET Norway Locationforecast 2.0 — ${now.time}*`,
        ].filter(Boolean);
        return { content: [{ type: "text", text: lines.join("\n") }] };
      } catch (err) {
        return { content: [{ type: "text", text: `Error: ${err.message}` }], isError: true };
      }
    }
  );

• src/index.js:112-135 (handler)

  Tool handler implementation: The async function that executes the tool logic - resolves location, fetches forecast from MET Norway API, extracts current weather data, and formats it into a readable markdown response.

  async ({ location }) => {
    try {
      const loc = await getLocation(location);
      const data = await fetchForecast(loc.lat, loc.lon);
      const now = data.properties.timeseries[0];
      const inst = now.data.instant.details;
      const symbol = now.data.next_1_hours?.summary?.symbol_code || now.data.next_6_hours?.summary?.symbol_code || "";
      const precip1h = now.data.next_1_hours?.details?.precipitation_amount;
      const lines = [
        `## ${loc.name} — Current Weather`,
        `**Conditions:** ${symbolToText(symbol)}`,
        `**Temperature:** ${inst.air_temperature}°C`,
        `**Humidity:** ${inst.relative_humidity}%`,
        `**Wind:** ${inst.wind_speed} m/s from ${inst.wind_from_direction}° (gusts ${inst.wind_speed_of_gust ?? "N/A"} m/s)`,
        `**Pressure:** ${inst.air_pressure_at_sea_level} hPa`,
        `**Cloud cover:** ${inst.cloud_area_fraction}%`,
        precip1h != null ? `**Precipitation (next hour):** ${precip1h} mm` : null,
        `\n*MET Norway Locationforecast 2.0 — ${now.time}*`,
      ].filter(Boolean);
      return { content: [{ type: "text", text: lines.join("\n") }] };
    } catch (err) {
      return { content: [{ type: "text", text: `Error: ${err.message}` }], isError: true };
    }
  }

• src/index.js:111-111 (schema)

  Input schema: Zod schema defining the location parameter as a required string describing Norwegian city name or lat,lon coordinates.

  { location: z.string().describe("Norwegian city name or lat,lon coordinates") },

• src/index.js:91-97 (helper)

  Helper function getLocation: Resolves user input to a location by checking known Norwegian cities or using geocoding API, throws error if location not found.

  async function getLocation(input) {
    const loc = resolveLocation(input);
    if (loc) return loc;
    const geo = await geocode(input);
    if (geo) return geo;
    throw new Error(`Could not find location "${input}" in Norway. Try a city name or lat,lon coordinates.`);
  }

• src/index.js:99-104 (helper)

  Helper function fetchForecast: Fetches weather forecast data from MET Norway Locationforecast 2.0 API for given latitude and longitude.

  async function fetchForecast(lat, lon) {
    const url = `${BASE_URL}/complete?lat=${lat.toFixed(4)}&lon=${lon.toFixed(4)}`;
    const res = await fetch(url, { headers: { "User-Agent": USER_AGENT } });
    if (!res.ok) throw new Error(`MET Norway API error (${res.status}): ${await res.text()}`);
    return res.json();
  }