What it does
Frankfurter is a hosted exchange-rate API that returns daily rate observations from central banks and other official sources. Its v2 REST interface can return a single currency pair, a date range, provider-specific data or a list of currencies, with JSON, CSV and newline-delimited JSON options. The public endpoint needs no API key; applications perform any amount conversion using the returned rate.
Ask for a rate, then do the arithmetic
The v2 documentation shows a direct route for one pair:
GET https://api.frankfurter.dev/v2/rate/eur/usd
That endpoint returns a date, base currency, quote currency and rate. A billing report could request the rate for the currencies and date it needs, then multiply the amount in its own code. For a historical series, the from, to and quotes parameters narrow the response; the docs also show CSV and NDJSON output for data exports or larger time ranges. These URLs are examples from the documentation, not API requests made for this record.
The public API is free and does not require registration or a key. It draws on daily central-bank and official-source data, with provider filters and attribution fields that help identify where a rate came from. If a workflow depends on a single authority, filter to that provider rather than relying on the default blended rate.
Frankfurter is not a live market feed: the project says it is not built for live trading, and update cadence can differ among sources. There is also no conversion endpoint; the client must apply the returned rate. Requests have no published daily or monthly quota, but the site says abuse-prevention rate limiting still applies. Direct provider queries may carry that provider's own terms.
Strengths
- The public endpoint requires no API key or sign-up and is described as free for commercial use.
- Historical series, provider filters, source attribution and CSV or NDJSON formats support more than a single current-rate lookup.
- The API returns dated rates rather than hiding the observation date behind a client-side conversion result.
Watch out for
- Rates update on a daily or source-specific schedule, and Frankfurter says the service is not designed for live trading.
- There is no conversion endpoint; the calling application must multiply by the returned rate.
Best for
- Displaying daily reference rates or currency conversions in billing, reporting and accounting workflows.
- Historical analysis that needs dated rates and the option to inspect contributing providers.
Sources
- Frankfurter | Free exchange rates API (Oct 25, 2026)