7 Best Free Currency Exchange APIs: The Complete Developer's Guide

async function convertCurrency(amount, from, to) {
  if (from === to) return amount;
  
  try {
    const host = 'api.frankfurter.dev';
    // Note: Frankfurter uses 'latest' endpoint. 
    // It auto-normalizes cross-rates if base is different from source.
    const resp = await fetch(`https://${host}/v1/latest?amount=${amount}&from=${from}&to=${to}`);
    
    if (!resp.ok) throw new Error(`API Error: ${resp.status}`);
    
    const data = await resp.json();
    return data.rates[to];
  } catch (error) {
    console.error("Conversion failed:", error);
    return null;
  }
}

// Usage: Convert 100 USD to JPY
convertCurrency(100, 'USD', 'JPY').then(rate => console.log(rate));

interface ExchangeResponse {
  result: string;
  base_code: string;
  conversion_rates: Record<string, number>;
}

async function getRates(apiKey: string): Promise<number | null> {
  const url = `https://v6.exchangerate-api.com/v6/${apiKey}/latest/USD`;
  
  const response = await fetch(url);
  const data: ExchangeResponse = await response.json();
  
  if (data.result === "success") {
    return data.conversion_rates['GBP'];
  }
  return null;
}

// Fetch formatted rates aimed at banking UI
fetch('https://api.currencyfreaks.com/v2.0/rates/latest?apikey=YOUR_KEY&symbols=BTC,ETH,USD')
  .then(response => response.json())
  .then(data => console.log(data.rates));

const redis = require('redis');
const client = redis.createClient();

async function getCachedRate(from, to) {
  const key = `rate:${from}:${to}`;
  
  // 1. Check Cache
  const cachedRate = await client.get(key);
  if (cachedRate) return parseFloat(cachedRate);
  
  // 2. Cache Miss: Fetch from API
  const freshRate = await fetchFromAPI(from, to);
  
  // 3. Set Cache with 1-hour Expiry (3600 seconds)
  await client.setEx(key, 3600, freshRate.toString());
  
  return freshRate;
}

const PROVIDERS = [
  { name: 'frankfurter', fn: callFrankfurter },
  { name: 'exchangerate', fn: callExchangeRate },
  { name: 'fallback_static', fn: getHardcodedRates } // Last resort
];

async function getRuggedRate() {
  for (const provider of PROVIDERS) {
    try {
      return await provider.fn();
    } catch (e) {
      console.warn(`${provider.name} failed, failing over...`);
    }
  }
}