MCP Weather Server

Instructions

Implementation Reference

• example-01/src/tools/getAlerts.ts:18-59 (handler)

  The handler function for the 'get_alerts' tool. Fetches active weather alerts from the National Weather Service API for a specified US state, handles errors and empty results, formats the alerts using formatAlert helper, and returns a formatted text response.

  async ({ state }) => {
    const stateCode = state.toUpperCase();
    const alertsUrl = `${CONFIG.NWS_API_BASE}/alerts?area=${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,
        },
      ],
    };
  },

• example-01/src/tools/getAlerts.ts:12-17 (schema)

  Input schema for the 'get_alerts' tool using Zod: requires a 2-character string for the US state code.

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

• example-01/src/tools/getAlerts.ts:8-60 (registration)

  Tool registration function that defines and registers the 'get_alerts' tool on an MCP server instance, including name, description, input schema, and handler.

  export const getAlertsTool = (server: McpServer) =>
    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 = `${CONFIG.NWS_API_BASE}/alerts?area=${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,
            },
          ],
        };
      },
    );

• example-01/src/index.ts:17-17 (registration)

  Invokes the getAlertsTool function to register the 'get_alerts' tool on the main MCP server.

  getAlertsTool(server);

• example-01/src/utils/index.ts:4-15 (helper)

  Helper function used by the get_alerts handler to format individual alert features into a readable string.

  // Format alert data
  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");
  }