Exchange rates.
No paywall.

# Get latest USD rates
curl "https://api.exchangerate.dev/v1/latest?base=USD" \
  -H "X-Api-Key: sk_live_your_key"

# Response
{
  "data": {
    "base": "USD",
    "date": "2026-03-31",
    "rates": {
      "EUR": 0.8697,
      "GBP": 0.7552,
      "BTC": 0.0000149
    }
  }
}

const res = await fetch(
  "https://api.exchangerate.dev/v1/convert?from=USD&to=EUR&amount=100",
  { headers: { "X-Api-Key": "sk_live_your_key" } }
);
const { data } = await res.json();

console.log(data);
// { from: "USD", to: "EUR", amount: 100, result: 86.97, rate: 0.8697 }

import requests

resp = requests.get(
    "https://api.exchangerate.dev/v1/timeseries",
    params={"base": "USD", "start": "2024-01-01", "end": "2024-01-31"},
    headers={"X-Api-Key": "sk_live_your_key"}
)

data = resp.json()["data"]
for date, rates in data["rates"].items():
    print(f"{date}: EUR={rates['EUR']:.4f}")