Starter MCP Server

Instructions

Implementation Reference

• src/tools/get-forecast.ts:22-96 (handler)

  The handler function that implements the 'get-forecast' tool logic. It fetches the NWS grid points for given lat/lon, retrieves the forecast data, formats the forecast periods, and returns a 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/tools/get-forecast.ts:13-20 (schema)

  Zod input schema defining latitude and longitude parameters for the tool.

  inputSchema: z.object({
    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/tools/get-forecast.ts:7-98 (registration)

  The registerGetForecast function that calls server.registerTool to register the 'get-forecast' tool with its schema and handler.

  export function registerGetForecast() {
    server.registerTool(
      'get-forecast',
      {
        title: 'Weather forecast',
        description: 'Get weather forecast for a location',
        inputSchema: z.object({
          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:10-10 (registration)

  The call to registerGetForecast() in the main index file, which triggers the tool registration.

  registerGetForecast()