Weather MCP Server

Instructions

Implementation Reference

• index.js:12-41 (handler)

  Core handler logic for fetching weather data from OpenWeatherMap API, formatting response as MCP content, and handling errors.

  async getWeather(city) {
    if (!this.apiKey) {
      throw new Error('OPENWEATHER_API_KEY environment variable is not set');
    }
    
    try {
      const response = await axios.get(
        `https://api.openweathermap.org/data/2.5/weather?q=${city}&appid=${this.apiKey}&units=metric`
      );
      const data = response.data;
      return {
        content: [{
          type: 'text',
          text: JSON.stringify({
            city: data.name,
            temperature: data.main.temp,
            description: data.weather[0].description,
          }, null, 2),
        }],
      };
    } catch (error) {
      return {
        content: [{
          type: 'text',
          text: `Error: ${error.message}`,
        }],
        isError: true,
      };
    }
  }

• index.js:52-57 (registration)

  Registers the 'getWeather' tool with the MCP server, including description, input schema, and an inline handler that delegates to WeatherService.getWeather.

  server.registerTool('getWeather', {
    description: 'Get current weather for a city',
    inputSchema: {
      city: z.string().describe('Name of the city'),
    },
  }, async ({ city }) => await weatherService.getWeather(city));

• index.js:54-56 (schema)

  Zod input schema defining the 'city' parameter as a required string.

  inputSchema: {
    city: z.string().describe('Name of the city'),
  },

• index.js:7-42 (helper)

  WeatherService class providing the getWeather method and managing the OpenWeather API key.

  class WeatherService {
    constructor(apiKey = process.env.OPENWEATHER_API_KEY) {
      this.apiKey = apiKey;
    }
  
    async getWeather(city) {
      if (!this.apiKey) {
        throw new Error('OPENWEATHER_API_KEY environment variable is not set');
      }
      
      try {
        const response = await axios.get(
          `https://api.openweathermap.org/data/2.5/weather?q=${city}&appid=${this.apiKey}&units=metric`
        );
        const data = response.data;
        return {
          content: [{
            type: 'text',
            text: JSON.stringify({
              city: data.name,
              temperature: data.main.temp,
              description: data.weather[0].description,
            }, null, 2),
          }],
        };
      } catch (error) {
        return {
          content: [{
            type: 'text',
            text: `Error: ${error.message}`,
          }],
          isError: true,
        };
      }
    }
  }