Weather MCP Server

Instructions

Implementation Reference

• index.js:204-257 (handler)

  The main handler function that fetches the 5-day weather forecast from the OpenWeatherMap API, groups data by day, computes high/low temps and dominant condition, and formats a textual response.

  async getWeatherForecast(city, units = 'metric') {
    const url = `${API_BASE_URL}/forecast?q=${encodeURIComponent(city)}&units=${units}&appid=${API_KEY}`;
  
    const response = await fetch(url);
  
    if (!response.ok) {
      if (response.status === 404) {
        throw new Error(`City "${city}" not found`);
      }
      throw new Error(`Weather API error: ${response.statusText}`);
    }
  
    const data = await response.json();
  
    // Format the response
    const tempUnit = units === 'metric' ? '°C' : '°F';
  
    // Group forecasts by day
    const dailyForecasts = {};
  
    data.list.forEach(item => {
      const date = new Date(item.dt * 1000).toLocaleDateString();
      if (!dailyForecasts[date]) {
        dailyForecasts[date] = [];
      }
      dailyForecasts[date].push(item);
    });
  
    // Build forecast text
    let forecastText = `📅 5-Day Weather Forecast for ${data.city.name}, ${data.city.country}\n\n`;
  
    Object.entries(dailyForecasts).slice(0, 5).forEach(([date, forecasts]) => {
      const temps = forecasts.map(f => f.main.temp);
      const maxTemp = Math.max(...temps);
      const minTemp = Math.min(...temps);
      const conditions = forecasts.map(f => f.weather[0].main);
      const mostCommon = conditions.sort((a,b) =>
        conditions.filter(v => v===a).length - conditions.filter(v => v===b).length
      ).pop();
  
      forecastText += `${date}:\n`;
      forecastText += `  High: ${maxTemp.toFixed(1)}${tempUnit} | Low: ${minTemp.toFixed(1)}${tempUnit}\n`;
      forecastText += `  Condition: ${mostCommon}\n\n`;
    });
  
    return {
      content: [
        {
          type: 'text',
          text: forecastText.trim(),
        },
      ],
    };
  }

• index.js:100-115 (schema)

  Input schema defining the required 'city' parameter and optional 'units' parameter (metric or imperial) for the tool.

  inputSchema: {
    type: 'object',
    properties: {
      city: {
        type: 'string',
        description: 'City name (e.g., "Taipei", "Tokyo", "New York")',
      },
      units: {
        type: 'string',
        description: 'Temperature units: "metric" (Celsius) or "imperial" (Fahrenheit)',
        enum: ['metric', 'imperial'],
        default: 'metric',
      },
    },
    required: ['city'],
  },

• index.js:97-116 (registration)

  Tool registration in the ListTools response, including name, description, and input schema.

  {
    name: 'get_weather_forecast',
    description: 'Get 5-day weather forecast for a specific city',
    inputSchema: {
      type: 'object',
      properties: {
        city: {
          type: 'string',
          description: 'City name (e.g., "Taipei", "Tokyo", "New York")',
        },
        units: {
          type: 'string',
          description: 'Temperature units: "metric" (Celsius) or "imperial" (Fahrenheit)',
          enum: ['metric', 'imperial'],
          default: 'metric',
        },
      },
      required: ['city'],
    },
  },

• index.js:129-130 (registration)

  Dispatch case in the CallToolRequestSchema handler that routes calls to the getWeatherForecast method.

  case 'get_weather_forecast':
    return await this.getWeatherForecast(args.city, args.units || 'metric');