#!/usr/bin/env node
import express from "express";
import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
import { StreamableHTTPServerTransport } from "@modelcontextprotocol/sdk/server/streamableHttp.js";
import { z } from "zod";
const NWS_API_BASE = "https://api.weather.gov";
const USER_AGENT = "weather-app/1.0";
// Function to create a new server instance for each request (stateless)
function createServer() {
const server = new McpServer({
name: "weather",
version: "1.0.0",
capabilities: {
resources: {},
tools: {},
},
});
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,
},
],
};
},
);
server.tool(
"get-forecast",
"Get weather forecast for a location",
{
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,
},
],
};
},
);
return server;
}
// Helper function for making NWS API requests
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;
}
}
interface AlertFeature {
properties: {
event?: string;
areaDesc?: string;
severity?: string;
status?: string;
headline?: string;
};
}
// Format alert data
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");
}
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[];
};
}
async function main() {
const app = express();
app.use(express.json());
// Handle POST requests for client-to-server communication (stateless mode)
app.post('/mcp', async (req, res) => {
// In stateless mode, create a new instance of transport and server for each request
// to ensure complete isolation. A single instance would cause request ID collisions
// when multiple clients connect concurrently.
try {
const server = createServer();
const transport = new StreamableHTTPServerTransport({
sessionIdGenerator: undefined, // Stateless mode
});
res.on('close', () => {
console.log('Request closed');
transport.close();
server.close();
});
await server.connect(transport);
await transport.handleRequest(req, res, req.body);
} catch (error) {
console.error('Error handling MCP request:', error);
if (!res.headersSent) {
res.status(500).json({
jsonrpc: '2.0',
error: {
code: -32603,
message: 'Internal server error',
},
id: null,
});
}
}
});
// SSE notifications not supported in stateless mode
app.get('/mcp', async (req, res) => {
console.log('Received GET MCP request');
res.writeHead(405).end(JSON.stringify({
jsonrpc: "2.0",
error: {
code: -32000,
message: "Method not allowed."
},
id: null
}));
});
// Session termination not needed in stateless mode
app.delete('/mcp', async (req, res) => {
console.log('Received DELETE MCP request');
res.writeHead(405).end(JSON.stringify({
jsonrpc: "2.0",
error: {
code: -32000,
message: "Method not allowed."
},
id: null
}));
});
// Start the server
const PORT = process.env.PORT || 3000;
app.listen(PORT, (error?: Error) => {
if (error) {
console.error('Failed to start server:', error);
process.exit(1);
}
console.log(`Weather MCP Stateless HTTP Server listening on port ${PORT}`);
console.log(`MCP endpoint: http://localhost:${PORT}/mcp`);
});
}
main().catch((error) => {
console.error("Fatal error in main():", error);
process.exit(1);
});
