Weather MCP Server

Instructions

Implementation Reference

• src/index.ts:150-223 (handler)

  The inline async handler function for the 'get-forecast' tool. It takes latitude and longitude, fetches grid points and forecast data from the National Weather Service API, formats the forecast periods, and returns them as text content.

  async ({ latitude, longitude }) => {
    // Get grid point data
    const pointsData = await makeNWSRequest<PointsResponse>(
      `/points/${latitude.toFixed(4)},${longitude.toFixed(4)}`
    );
  
    if (!pointsData) {
      return {
        content: [
          {
            type: "text",
            text: `Failed to retrieve grid point data for coordinates: ${latitude}, ${longitude}. This location may not be supported by the NWS API (only US locations are supported).`,
          },
        ],
      };
    }
  
    const forecastUrl = pointsData.properties?.forecast;
    if (!forecastUrl) {
      return {
        content: [
          {
            type: "text",
            text: "Failed to get forecast URL from grid point data",
          },
        ],
      };
    }
  
    // Get forecast data - using full URL since the forecast URL is absolute
    const forecastData = await makeNWSRequest<ForecastResponse>(forecastUrl);
    if (!forecastData) {
      return {
        content: [
          {
            type: "text",
            text: "Failed to retrieve forecast data",
          },
        ],
      };
    }
  
    const periods = forecastData.properties?.periods || [];
    if (periods.length === 0) {
      return {
        content: [
          {
            type: "text",
            text: "No forecast periods available",
          },
        ],
      };
    }
  
    // Format forecast periods
    const formattedForecast = periods.map((period: ForecastPeriod) =>
      [
        `${period.name || "Unknown"}:`,
        `Temperature: ${period.temperature || "Unknown"}°${period.temperatureUnit || "F"}`,
        `Wind: ${period.windSpeed || "Unknown"} ${period.windDirection || ""}`,
        `${period.shortForecast || "No forecast available"}`,
        "---",
      ].join("\n"),
    );
  
    return {
      content: [
        {
          type: "text",
          text: formattedForecast.join("\n"),
        },
      ],
    };
  },

• src/index.ts:146-149 (schema)

  Zod input schema for the 'get-forecast' tool, validating latitude and longitude parameters.

  {
    latitude: z.number().min(-90).max(90).describe("Latitude of the location"),
    longitude: z.number().min(-180).max(180).describe("Longitude of the location"),
  },

• src/index.ts:143-224 (registration)

  Registration of the 'get-forecast' tool on the MCP server, specifying name, description, input schema, and handler.

  server.tool(
    "get-forecast",
    "Get weather forecast for a location",
    {
      latitude: z.number().min(-90).max(90).describe("Latitude of the location"),
      longitude: z.number().min(-180).max(180).describe("Longitude of the location"),
    },
    async ({ latitude, longitude }) => {
      // Get grid point data
      const pointsData = await makeNWSRequest<PointsResponse>(
        `/points/${latitude.toFixed(4)},${longitude.toFixed(4)}`
      );
  
      if (!pointsData) {
        return {
          content: [
            {
              type: "text",
              text: `Failed to retrieve grid point data for coordinates: ${latitude}, ${longitude}. This location may not be supported by the NWS API (only US locations are supported).`,
            },
          ],
        };
      }
  
      const forecastUrl = pointsData.properties?.forecast;
      if (!forecastUrl) {
        return {
          content: [
            {
              type: "text",
              text: "Failed to get forecast URL from grid point data",
            },
          ],
        };
      }
  
      // Get forecast data - using full URL since the forecast URL is absolute
      const forecastData = await makeNWSRequest<ForecastResponse>(forecastUrl);
      if (!forecastData) {
        return {
          content: [
            {
              type: "text",
              text: "Failed to retrieve forecast data",
            },
          ],
        };
      }
  
      const periods = forecastData.properties?.periods || [];
      if (periods.length === 0) {
        return {
          content: [
            {
              type: "text",
              text: "No forecast periods available",
            },
          ],
        };
      }
  
      // Format forecast periods
      const formattedForecast = periods.map((period: ForecastPeriod) =>
        [
          `${period.name || "Unknown"}:`,
          `Temperature: ${period.temperature || "Unknown"}°${period.temperatureUnit || "F"}`,
          `Wind: ${period.windSpeed || "Unknown"} ${period.windDirection || ""}`,
          `${period.shortForecast || "No forecast available"}`,
          "---",
        ].join("\n"),
      );
  
      return {
        content: [
          {
            type: "text",
            text: formattedForecast.join("\n"),
          },
        ],
      };
    },
  );

• src/index.ts:29-45 (helper)

  Helper function used by the get-forecast handler to make API requests to the NWS weather service with axios and error handling.

  async function makeNWSRequest<T>(url: string): Promise<T | null> {
    try {
      const response = await api.get<T>(url);
      return response.data;
    } catch (error) {
      if (axios.isAxiosError(error)) {
        console.error("Error making NWS request:", error.message);
        if (error.response) {
          console.error("Response status:", error.response.status);
          console.error("Response data:", error.response.data);
        }
      } else {
        console.error("Unexpected error:", error);
      }
      return null;
    }
  }

• src/index.ts:83-93 (schema)

  TypeScript interfaces defining the structure of NWS API responses used in the get-forecast handler (PointsResponse and ForecastResponse). Also nearby ForecastPeriod (70-77).

  interface PointsResponse {
    properties: {
      forecast?: string;
    };
  }
  
  interface ForecastResponse {
    properties: {
      periods: ForecastPeriod[];
    };
  }

• src/index.ts:70-77 (schema)

  TypeScript interface for ForecastPeriod used in parsing forecast data.

  interface ForecastPeriod {
    name?: string;
    temperature?: number;
    temperatureUnit?: string;
    windSpeed?: string;
    windDirection?: string;
    shortForecast?: string;
  }