Fiat Agent vs Frankfurter

The short version

Frankfurter is the honest answer to a lot of searches for a free currency API: no key, no account, no billing, open source, and reference rates from central banks and official sources. If all you need is a daily reference figure for a chart or a calculator, it is hard to beat free.

The trade-off is cadence and control. Central-bank reference rates are published once per business day, so intraday movement is not visible; there is no account, so there is no per-account balance, key rotation or usage record. Fiat Agent exists for the cases where those things matter — and it also has an open endpoint, so you can compare them without signing up for anything.

When Frankfurter is the right call

If your page shows yesterday's official rate, or a chart of monthly averages, then a daily central-bank reference figure is exactly the semantics you want — and paying for anything else would be a mistake.

It is also the only option here you can self-host, which some teams require for compliance reasons. That is a real advantage no hosted API can match.

When a stored, metered reading helps

Two things get harder with a public, unmetered endpoint: knowing how old a figure is, and knowing which of your systems used it. Fiat Agent stores each reading before serving it and returns the timestamp of that reading, so a displayed price can always be traced to the moment it was taken.

The other difference is operational: keys you can revoke per environment, a balance that tells you what a service is consuming, and responses that fail loudly with typed error codes rather than an empty object.

const res = await fetch("https://fiatagent.base44.app/api/v1/public/rates");
const { meta, data } = await res.json();

const ageMinutes = Math.round((Date.now() - new Date(meta.updated_at)) / 60000);
console.log(data.latest.rates.EUR, "EUR per USD, read", ageMinutes, "minutes ago");

Trying both costs nothing

Frankfurter needs no signup, and neither does Fiat Agent's open endpoint. Fetch the same pair from both, compare the figures against the official source, and pick the one whose cadence matches what you display. That is a ten-minute decision, not a procurement exercise.