IconVault's IBAN Validator checks any International Bank Account Number with the official mod-97 checksum algorithm from ISO 13616. Paste an IBAN and instantly see whether it is valid, which country it belongs to, and the parsed bank code and account number inside it.

You can also format IBANs for print (groups of four) or compact electronic use, and browse per-country IBAN structure rows. It is free, needs no signup, and runs fully in your browser, so account numbers never leave your device. Honest note: a valid checksum only proves the IBAN is well-formed; it does not prove the account exists or belongs to anyone.