Weather MCP

Instructions

Implementation Reference

• src/index.ts:33-72 (handler)

  Executes the get-alerts tool: fetches weather alerts from NWS API for a given state code, handles errors and empty results, formats alerts using helper functions, and returns formatted text content.

  async ({ state }) => {
      const stateCode = state.toUpperCase();
      const alertsUrl = `${NWS_API_BASE}/alerts?area=${stateCode}`;
      const alertsData = await makeNWSRequest<AlertsResponse>(alertsUrl);
  
      if (!alertsData) {
          return {
              content: [
                  {
                      type: "text",
                      text: "Failed to retrieve alerts data",
                  },
              ],
          };
      }
  
      const features = alertsData.features || [];
      if (features.length === 0) {
          return {
              content: [
                  {
                      type: "text",
                      text: `No active alerts for ${stateCode}`,
                  },
              ],
          };
      }
  
      const formattedAlerts = features.map(formatAlert);
      const alertsText = `Active alerts for ${stateCode}:\n\n${formattedAlerts.join("\n")}`;
  
      return {
          content: [
              {
                  type: "text",
                  text: alertsText,
              },
          ],
      };
  },

• src/index.ts:27-73 (registration)

  Registers the 'get-alerts' tool with the MCP server, specifying name, description, input schema, and handler function.

  server.tool(
      "get-alerts",
      "Get weather alerts for a state",
      {
          state: z.string().length(2).describe("Two-letter state code (e.g. CA, NY)"),
      },
      async ({ state }) => {
          const stateCode = state.toUpperCase();
          const alertsUrl = `${NWS_API_BASE}/alerts?area=${stateCode}`;
          const alertsData = await makeNWSRequest<AlertsResponse>(alertsUrl);
  
          if (!alertsData) {
              return {
                  content: [
                      {
                          type: "text",
                          text: "Failed to retrieve alerts data",
                      },
                  ],
              };
          }
  
          const features = alertsData.features || [];
          if (features.length === 0) {
              return {
                  content: [
                      {
                          type: "text",
                          text: `No active alerts for ${stateCode}`,
                      },
                  ],
              };
          }
  
          const formattedAlerts = features.map(formatAlert);
          const alertsText = `Active alerts for ${stateCode}:\n\n${formattedAlerts.join("\n")}`;
  
          return {
              content: [
                  {
                      type: "text",
                      text: alertsText,
                  },
              ],
          };
      },
  );

• src/index.ts:30-32 (schema)

  Zod schema for input validation: requires a 2-letter state code.

  {
      state: z.string().length(2).describe("Two-letter state code (e.g. CA, NY)"),
  },

• src/helper.ts:32-42 (helper)

  Helper function to format an individual alert feature into a multi-line string summary.

  export function formatAlert(feature: AlertFeature): string {
      const props = feature.properties;
      return [
          `Event: ${props.event || "Unknown"}`,
          `Area: ${props.areaDesc || "Unknown"}`,
          `Severity: ${props.severity || "Unknown"}`,
          `Status: ${props.status || "Unknown"}`,
          `Headline: ${props.headline || "No headline"}`,
          "---",
      ].join("\n");
  }

• src/helper.ts:2-19 (helper)

  Generic helper for making authenticated fetch requests to NWS API endpoints.

  export async function makeNWSRequest<T>(url: string): Promise<T | null> {
      const USER_AGENT = "weather-app/1.0";
      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/helper.ts:53-55 (schema)

  TypeScript interface defining the structure of the NWS alerts API response.

  export interface AlertsResponse {
      features: AlertFeature[];
  }