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Overview

File: src/tools/GetWeatherTool.ts The Weather Tool demonstrates external API integration using the free Open-Meteo API (no API key required).

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What It Does

  • Fetches real-time weather for any city worldwide
  • Two-step process: geocoding + weather data
  • Error handling for invalid cities
  • No API key or authentication required

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Complete Code

import { LuaTool } from 'lua-cli';
import { z } from 'zod';

export default class GetWeatherTool implements LuaTool {
  name = "get_weather";
  description = "Get current weather conditions for any city";
  
  inputSchema = z.object({
    city: z.string().describe("City name (e.g., 'London', 'Tokyo')")
  });

  async execute(input: z.infer<typeof this.inputSchema>) {
    // Step 1: Convert city name to coordinates
    const geoUrl = `https://geocoding-api.open-meteo.com/v1/search?name=${encodeURIComponent(input.city)}&count=1`;
    const geoRes = await fetch(geoUrl);
    const geoData = await geoRes.json();
    
    if (!geoData.results?.[0]) {
      throw new Error(`City not found: ${input.city}`);
    }
    
    const { latitude, longitude, name } = geoData.results[0];
    
    // Step 2: Get weather for coordinates
    const weatherUrl = `https://api.open-meteo.com/v1/forecast?latitude=${latitude}&longitude=${longitude}&current_weather=true`;
    const weatherRes = await fetch(weatherUrl);
    const weatherData = await weatherRes.json();
    
    return {
      city: name,
      temperature: weatherData.current_weather.temperature,
      windSpeed: weatherData.current_weather.windspeed,
      weatherCode: weatherData.current_weather.weathercode
    };
  }
}

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Key Concepts

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1. Two-Step API Call

Why? Weather APIs need coordinates, but users provide city names. 
// Step 1: City name → Coordinates
const geoData = await fetch(geocodingUrl);
const { latitude, longitude } = geoData.results[0];

// Step 2: Coordinates → Weather
const weatherData = await fetch(weatherUrl);

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2. URL Encoding

Always encode user input in URLs: 
const geoUrl = `https://geocoding-api.open-meteo.com/v1/search?name=${encodeURIComponent(input.city)}&count=1`;

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3. Error Handling

Check if city exists before proceeding: 
if (!geoData.results?.[0]) {
  throw new Error(`City not found: ${input.city}`);
}

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4. Structured Return

Return organized data, not raw API response: 
return {
  city: name,              // Clean city name
  temperature: data.temp,  // Extract what's needed
  windSpeed: data.wind     // No extra data
};

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Testing

lua test
Try different cities:
  • London - Should work
  • Tokyo - Should work
  • New York - Should work
  • XYZ123 - Should fail gracefully

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Customization Ideas

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Add Temperature Units

inputSchema = z.object({
  city: z.string(),
  units: z.enum(['metric', 'imperial']).default('metric')
});

// In URL
const weatherUrl = `...&temperature_unit=${units === 'imperial' ? 'fahrenheit' : 'celsius'}`;

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Add Weather Recommendations

return {
  ...weatherData,
  recommendation: temperature < 10 
    ? "🧥 Bring a warm jacket"
    : temperature < 20
    ? "👕 Light jacket recommended"
    : "☀️ T-shirt weather!"
};

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Add Forecast

const forecastUrl = `...&forecast_days=7`;
const forecast = await fetch(forecastUrl);

return {
  current: {...},
  forecast: forecast.daily
};

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What You’ll Learn

External APIs

How to call external REST APIs

Error Handling

Graceful error messages

Data Transformation

Converting API responses to clean output

URL Encoding

Safely encoding user input in URLs

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Next Steps

User Data Example

Learn platform API usage

Payment Example

See authenticated external API