MCP Weather Server

Instructions

Implementation Reference

• src/index.ts:147-227 (handler)

  Handler function that fetches weather grid points, retrieves forecast data from NWS API, formats periods with temperature, wind, and short forecast, and returns formatted 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 validating latitude (-90 to 90) and longitude (-180 to 180) 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:136-228 (registration)

  Full tool registration 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:19-35 (helper)

  Helper function to make authenticated fetch requests to the National Weather Service (NWS) API, handling errors and returning typed JSON or null.

  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;
    }
  }