Convert an amount between currencies at the official European Central Bank reference rate. Answers "what is the USD to EUR exchange rate", "convert 250 GBP to JPY", "what was the EUR/USD FX rate on 2024-03-15". Multi-currency in one call (to=EUR,GBP,JPY), 30+ currencies, historical daily fixings back to 1999. Deterministic and cacheable: real ECB data, not a model estimate — identical inputs always return the identical rate. Keyless, sub-second.