Weather MCP Server

Instructions

Implementation Reference

• src/index.ts:136-228 (registration)

  Registration of the 'get-forecast' tool using server.tool(), including name, description, input schema, and inline handler function.

  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 pointsUrl = `${NWS_API_BASE}/points/${latitude.toFixed(
        4
      )},${longitude.toFixed(4)}`;
      const pointsData = await makeNWSRequest<PointsResponse>(pointsUrl);
  
      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
      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")
      );
  
      const forecastText = `Forecast for ${latitude}, ${longitude}:\n\n${formattedForecast.join(
        "\n"
      )}`;
  
      return {
        content: [
          {
            type: "text",
            text: forecastText,
          },
        ],
      };
    }
  );

• src/index.ts:147-227 (handler)

  The core handler logic for the 'get-forecast' tool. Fetches grid points, forecast data from NWS API, handles errors, formats forecast periods into text response.

  async ({ latitude, longitude }) => {
    // Get grid point data
    const pointsUrl = `${NWS_API_BASE}/points/${latitude.toFixed(
      4
    )},${longitude.toFixed(4)}`;
    const pointsData = await makeNWSRequest<PointsResponse>(pointsUrl);
  
    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
    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")
    );
  
    const forecastText = `Forecast for ${latitude}, ${longitude}:\n\n${formattedForecast.join(
      "\n"
    )}`;
  
    return {
      content: [
        {
          type: "text",
          text: forecastText,
        },
      ],
    };
  }

• src/index.ts:139-146 (schema)

  Zod input schema defining parameters latitude (number -90 to 90) and longitude (number -180 to 180) for the tool.

  {
    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:19-35 (helper)

  Helper utility function used by the get-forecast handler to make API requests to the National Weather Service (NWS) with appropriate headers and error handling.

  async function makeNWSRequest<T>(url: string): Promise<T | null> {
    const headers = {
      "User-Agent": USER_AGENT,
      Accept: "application/geo+json",
    };
  
    try {
      const response = await fetch(url, { headers });
      if (!response.ok) {
        throw new Error(`HTTP error! status: ${response.status}`);
      }
      return (await response.json()) as T;
    } catch (error) {
      console.error("Error making NWS request:", error);
      return null;
    }
  }