Fiat Agent vs Open Exchange Rates

The short version

Open Exchange Rates has one of the friendliest free tiers in the category: a thousand requests a month, hourly updates and access to historical data, with paid plans starting at $12 a month. It is a common first choice for a prototype, because the free plan actually works.

The trade-offs appear as a project grows: the free tier quotes against USD only, the allowance resets monthly, and history is reached through its own endpoint shape. Fiat Agent takes a different route — any base currency on both endpoints, a balance that does not reset, and history read from the same response as the current rates.

One base currency, or any base currency

Quoting against USD is fine until a page needs to show the price in euros and the rate you fetched needs a division on every render. Fiat Agent accepts ?base= on both endpoints, so the reading arrives already quoted the way the page displays it.

If you do get USD-based quotes, the arithmetic for any pair is a single division rather than a second lookup: rate(A→B) = quote(B) ÷ quote(A).

const { data } = await res.json();
const rate = (from, to) => data.latest.rates[to] / data.latest.rates[from];

const total = 199.95;
console.log(
  total.toLocaleString("en-US", { style: "currency", currency: "GBP" }),
  "≈",
  (total * rate("USD", "GBP")).toFixed(2),
  "GBP",
);

What a monthly reset buys and costs

A monthly allowance is good for steady workloads: the same thousand calls every month, predictable. It is less good for a service that is busy at launch and quiet afterwards, where most of the allowance simply evaporates.

A one-time balance behaves the opposite way: nothing expires, so a quiet month costs nothing; a loud one spends what you bought. The honest rule is that a monthly plan wins when you genuinely use most of it every month.

History without a second endpoint

In Fiat Agent, history is not a separate resource to learn. A keyed call accepts ?from= and ?to= as UTC calendar days, and the same response still carries the current reading, the catalogue and the account balance. One HTTP round trip, one shape to parse.