A Sinatra extension wrapping the UniRate API (https://unirateapi.com) — free currency exchange rates, conversion, supported-currency listings, and VAT rates. Registers via `register Sinatra::UniRate` in classic or modular apps, exposes settings-based configuration, route/view helpers (unirate_rate, unirate_convert, unirate_currencies, unirate_vat), an optional JSON proxy mount, and a stdlib-only client with full error mapping. Zero runtime dependencies beyond Sinatra.