Demo Run Your First MCP Tool Weather Tool

curl "https://api.open-meteo.com/v1/forecast?latitude=52.52&longitude=13.41&current_weather=true&hourly=temperature_2m,relativehumidity_2m,windspeed_10m"

git clone https://github.com/JeremyMorgan/Weather-MCP-Server
cd Weather-MCP-Server
npm install
npm run dev

#!/usr/bin/env node

import { Server } from '@modelcontextprotocol/sdk/server/index.js';
import { StdioServerTransport } from '@modelcontextprotocol/sdk/server/stdio.js';
import { RequestSchema } from '@modelcontextprotocol/sdk/types.js';
import { z } from 'zod';
import fetch from 'node-fetch';

// Weather API base URL
const WEATHER_API_BASE = 'https://api.open-meteo.com/v1/forecast';

// Tool definitions (exposed to MCP clients)
const tools = [
  {
    name: 'get_current_weather',
    description: 'Get current weather data for a specific location',
    inputSchema: {
      type: 'object',
      properties: {
        latitude: { type: 'number', description: 'Latitude of the location' },
        longitude: { type: 'number', description: 'Longitude of the location' }
      },
      required: ['latitude', 'longitude']
    }
  },
  {
    name: 'get_weather_forecast',
    description: 'Get hourly weather forecast for a specific location',
    inputSchema: {
      type: 'object',
      properties: {
        latitude: { type: 'number', description: 'Latitude of the location' },
        longitude: { type: 'number', description: 'Longitude of the location' },
        days: { type: 'number', description: 'Number of days to forecast (default: 7)' }
      },
      required: ['latitude', 'longitude']
    }
  },
  {
    name: 'get_weather_summary',
    description: 'Get a short natural-language summary for a location',
    inputSchema: {
      type: 'object',
      properties: {
        latitude: { type: 'number' },
        longitude: { type: 'number' }
      },
      required: ['latitude', 'longitude']
    }
  }
];

// Helper functions implementing tool behavior
async function getCurrentWeather({ latitude, longitude }) {
  const url = `${WEATHER_API_BASE}?latitude=${latitude}&longitude=${longitude}&current_weather=true`;
  const res = await fetch(url);
  const data = await res.json();
  return data.current_weather || data;
}

async function getWeatherForecast({ latitude, longitude, days = 7 }) {
  // Request hourly temperature, relative humidity, and windspeed covering the requested days
  const hourly = 'temperature_2m,relativehumidity_2m,windspeed_10m';
  // Open-Meteo typically supports start_date/end_date for precise ranges; here we request hourly data and use forecast_days to limit days when available.
  const url = `${WEATHER_API_BASE}?latitude=${latitude}&longitude=${longitude}&hourly=${hourly}&forecast_days=${days}`;
  const res = await fetch(url);
  return await res.json();
}

async function getWeatherSummary({ latitude, longitude }) {
  const current = await getCurrentWeather({ latitude, longitude });
  const forecast = await getWeatherForecast({ latitude, longitude, days: 1 });
  const temp = current.temperature ?? current.temp ?? 'unknown';
  const wind = current.windspeed ?? current.wind_speed ?? 'unknown';
  const humidity = forecast.hourly?.relativehumidity_2m?.[0] ?? 'unknown';
  return {
    summary: `Current temperature ${temp}°C, wind ${wind} m/s, humidity ${humidity}%.`,
    current,
    forecast
  };
}

// Map of tool names to handlers
const toolHandlers = {
  get_current_weather: getCurrentWeather,
  get_weather_forecast: getWeatherForecast,
  get_weather_summary: getWeatherSummary
};

// Create the MCP server with stdio transport
const server = new Server(
  { name: 'weather-mcp-server', version: '1.0.0' },
  {
    transport: new StdioServerTransport(),
    capabilities: { tools } // advertise the tools
  }
);

// Request schemas for MCP messages
const ToolsCallRequestSchema = RequestSchema.extend({
  method: z.literal('tools/call'),
  params: z.object({
    name: z.string(),
    arguments: z.record(z.any())
  })
});

const ToolsListRequestSchema = RequestSchema.extend({
  method: z.literal('tools/list'),
  params: z.object({}).optional()
});

// Handler to list available tools
server.setRequestHandler(ToolsListRequestSchema, async () => {
  return { result: { tools } };
});

// Handler to call a tool
server.setRequestHandler(ToolsCallRequestSchema, async (request) => {
  const { name, arguments: args } = request.params;
  const handler = toolHandlers[name];
  if (!handler) {
    throw new Error(`Tool "${name}" not found`);
  }
  const result = await handler(args);
  return { result };
});

// Start listening
server.start().catch((err) => {
  console.error('Server failed to start:', err);
  process.exit(1);
});

node /Users/jeremy/demos/Weather-MCP-Server/server.js

{
  "method": "tools/call",
  "params": {
    "name": "get_current_weather",
    "arguments": {
      "latitude": 45.4318,
      "longitude": -123.1426
    }
  }
}

curl "https://api.open-meteo.com/v1/forecast?latitude=45.4318&longitude=-123.1426&hourly=temperature_2m,relativehumidity_2m"

{
  "mcpServers": {
    "Hacker News API": {
      "command": "/usr/local/bin/node",
      "args": ["/Users/jeremy/demos/postman-mcp-server/mcpServer.js"]
    },
    "Meteo API": {
      "command": "/usr/local/bin/node",
      "args": ["/Users/jeremy/demos/Weather-MCP-Server/server.js"]
    }
  }
}