Weather MCP Server

Instructions

Implementation Reference

• src/index.ts:96-141 (registration)

  Registration of the 'get-alerts' MCP tool, including input schema and inline handler function that fetches and formats weather alerts for a US state.

  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 alertsData = await makeNWSRequest<AlertsResponse>(`/alerts?area=${stateCode}`);
  
      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:102-140 (handler)

  The handler function for 'get-alerts' tool: fetches alerts from National Weather Service API using the provided state code, handles errors/no data, formats alerts using helper, and returns formatted text content.

  async ({ state }) => {
    const stateCode = state.toUpperCase();
    const alertsData = await makeNWSRequest<AlertsResponse>(`/alerts?area=${stateCode}`);
  
    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:99-101 (schema)

  Input schema for 'get-alerts' tool using Zod: requires a 2-letter state code.

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

• src/index.ts:58-68 (helper)

  Helper function to format individual alert feature into a readable string.

  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/index.ts:29-45 (helper)

  Helper function to make API requests to the National Weather Service with error handling using axios.

  async function makeNWSRequest<T>(url: string): Promise<T | null> {
    try {
      const response = await api.get<T>(url);
      return response.data;
    } catch (error) {
      if (axios.isAxiosError(error)) {
        console.error("Error making NWS request:", error.message);
        if (error.response) {
          console.error("Response status:", error.response.status);
          console.error("Response data:", error.response.data);
        }
      } else {
        console.error("Unexpected error:", error);
      }
      return null;
    }
  }