IBAN
Bank accounts with a built-in checksum.
Where it came from
IBAN (International Bank Account Number) was created by the European Committee for Banking Standards in the 1990s and standardized as ISO 13616, to make cross-border payments reliable. Before it, every country had its own account format and transfers failed constantly.
Today over 80 countries use IBAN, from Germany's DE to Russia's RU and Saudi Arabia's SA. The US still mostly does not.
How it works
An IBAN is up to 34 characters: a two-letter country code, two check digits, then the national account. The magic is MOD-97: rearrange and treat it as a number, divide by 97, and the remainder must be 1 — that catches almost all typos.
UWC validates and reformats IBANs (grouping into fours) in your browser, checking the checksum without sending anything.