MCP Server Example

Instructions

Implementation Reference

• src/index.ts:142-216 (handler)

  The core handler function for the 'get-forecast' tool. It takes latitude and longitude, fetches the NWS grid points to get the forecast URL, then fetches the forecast data, formats each period's details (name, temp, wind, shortForecast), and returns a formatted text response. Handles various error cases by returning error messages.
  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:138-141 (schema)

  Input schema using Zod for 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:135-137 (registration)

  Registration of the 'get-forecast' tool on the MCP server, specifying the tool name and description.
  server.tool( "get-forecast", "Get weather forecast for a location",
• src/index.ts:19-35 (helper)

  Reusable helper function for making authenticated fetch requests to the NWS API, returning typed JSON or null on error. Used twice in the get-forecast handler.
  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; } }
• src/index.ts:61-85 (schema)

  TypeScript interfaces defining the structure of NWS API responses used in the get-forecast tool (ForecastPeriod, PointsResponse, ForecastResponse).
  interface ForecastPeriod { name?: string; temperature?: number; temperatureUnit?: string; windSpeed?: string; windDirection?: string; shortForecast?: string; } interface AlertsResponse { features: AlertFeature[]; } interface PointsResponse { properties: { forecast?: string; }; } interface ForecastResponse { properties: { periods: ForecastPeriod[]; }; }