Fiat Agent vs Fixer

The short version

Fixer is one of the longest-running currency APIs, and it is a good fit when you want a subscription with a predictable monthly volume and a long published history behind it. Its plan structure is a monthly one: a capped free tier, then larger monthly call volumes as you pay more.

Fiat Agent is built the other way round. There is no monthly allowance to exhaust and no reset date — you get an open endpoint with no key for evaluation, a one-time signup bonus when you create an account, and one-time packs if you ever need more. This page sets out where each model helps, using both vendors' own published numbers.

The real difference is the billing shape, not the JSON

Both services return JSON over HTTPS and both let you pick a base currency, so the integration work is comparable. What changes is what happens in a quiet month and in a loud one: a subscription bill arrives whether or not you called, while a one-time balance sits still until you use it.

That matters most for a project whose traffic is spiky — a storefront that quotes prices for a launch week, an internal tool used a few days a month, or a side project that may or may not grow. A monthly plan is efficient only when it is steady.

History on both sides, reached differently

Fixer publishes historical data as part of its plans. Fiat Agent keeps every reading it has ever stored and lets a keyed call ask for a UTC date range directly: ?from=2026-01-01&to=2026-03-31 returns the readings in that span, both ends inclusive.

Neither service is a tick feed. If you need intraday execution prices, you need a market-data vendor rather than a reference-rate API — Fiat Agent publishes indicative reference readings, and says so on every response.

Switching, or running both for a week

Moving off a key-in-the-query-string API is a small change: send the credential as a bearer header instead and reshape two field names. Running both side by side for a week is the honest way to decide, and the open endpoint makes that free.

const url = new URL("https://fiatagent.base44.app/api/v1/rates");
url.searchParams.set("base", "USD");
url.searchParams.set("from", "2026-10-01");
url.searchParams.set("to", "2026-10-31");

const res = await fetch(url, {
  headers: { Authorization: "Bearer " + process.env.FIAT_AGENT_KEY },
});

if (!res.ok) throw new Error("Fiat Agent: " + res.status);

const { meta, data } = await res.json();
const eurPerUsd = data.latest.rates.EUR;
const gbpPerEur = data.latest.rates.GBP / data.latest.rates.EUR;