mcp-norwegian-weather

Instructions

Implementation Reference

• src/index.js:138-166 (registration)

  Registration of weather_forecast tool with the MCP server, including the schema definition (location and hours parameters) and the handler function

  server.tool(
    "weather_forecast",
    "Get hourly weather forecast for a location in Norway using MET Norway (yr.no).",
    {
      location: z.string().describe("Norwegian city name or lat,lon coordinates"),
      hours: z.number().min(1).max(72).optional().describe("Hours ahead (default 24, max 72)"),
    },
    async ({ location, hours }) => {
      try {
        const loc = await getLocation(location);
        const data = await fetchForecast(loc.lat, loc.lon);
        const maxHours = hours || 24;
        const slice = data.properties.timeseries.slice(0, maxHours);
        const lines = [`## ${loc.name} — ${maxHours}h Forecast\n`];
        for (const entry of slice) {
          const t = new Date(entry.time);
          const time = t.toLocaleString("nb-NO", { timeZone: "Europe/Oslo", weekday: "short", day: "numeric", month: "short", hour: "2-digit", minute: "2-digit" });
          const inst = entry.data.instant.details;
          const symbol = entry.data.next_1_hours?.summary?.symbol_code || entry.data.next_6_hours?.summary?.symbol_code || "";
          const precip = entry.data.next_1_hours?.details?.precipitation_amount;
          lines.push(`**${time}:** ${inst.air_temperature}°C, ${symbolToText(symbol)}, wind ${inst.wind_speed} m/s${precip != null ? `, ${precip} mm` : ""}`);
        }
        lines.push(`\n*MET Norway Locationforecast 2.0*`);
        return { content: [{ type: "text", text: lines.join("\n") }] };
      } catch (err) {
        return { content: [{ type: "text", text: `Error: ${err.message}` }], isError: true };
      }
    }
  );

• src/index.js:145-165 (handler)

  The main handler logic for weather_forecast tool that fetches forecast data, processes hourly entries, and formats output with temperature, weather conditions, wind, and precipitation

  async ({ location, hours }) => {
    try {
      const loc = await getLocation(location);
      const data = await fetchForecast(loc.lat, loc.lon);
      const maxHours = hours || 24;
      const slice = data.properties.timeseries.slice(0, maxHours);
      const lines = [`## ${loc.name} — ${maxHours}h Forecast\n`];
      for (const entry of slice) {
        const t = new Date(entry.time);
        const time = t.toLocaleString("nb-NO", { timeZone: "Europe/Oslo", weekday: "short", day: "numeric", month: "short", hour: "2-digit", minute: "2-digit" });
        const inst = entry.data.instant.details;
        const symbol = entry.data.next_1_hours?.summary?.symbol_code || entry.data.next_6_hours?.summary?.symbol_code || "";
        const precip = entry.data.next_1_hours?.details?.precipitation_amount;
        lines.push(`**${time}:** ${inst.air_temperature}°C, ${symbolToText(symbol)}, wind ${inst.wind_speed} m/s${precip != null ? `, ${precip} mm` : ""}`);
      }
      lines.push(`\n*MET Norway Locationforecast 2.0*`);
      return { content: [{ type: "text", text: lines.join("\n") }] };
    } catch (err) {
      return { content: [{ type: "text", text: `Error: ${err.message}` }], isError: true };
    }
  }

• src/index.js:99-104 (helper)

  fetchForecast helper function that makes the actual API call to MET Norway Locationforecast 2.0 API to retrieve weather data for given coordinates

  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();
  }

• src/index.js:91-97 (helper)

  getLocation helper function that resolves location input (city name or lat,lon coordinates) to actual coordinates using predefined cities or geocoding API

  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:63-67 (helper)

  symbolToText helper function that converts MET Norway weather symbol codes to human-readable weather condition descriptions

  function symbolToText(symbol) {
    if (!symbol) return "Unknown";
    const base = symbol.replace(/_(day|night|polartwilight)$/, "");
    return SYMBOL_MAP[base] || base;
  }