Validation

Format and check-digit validation: IBANs of 87 countries (ISO 13616: country, length, mod-97; Turkish IBANs name their bank from the central bank's payment-systems participant list), Turkish national ids and foreigners' ids (TCKN/YKN), tax numbers (VKN), and Turkish phone numbers (E.164 and national form, and whether mobile, landline, toll-free or 444).

Only the number's form is checked: nothing is looked up, stored or cached. A valid id or tax number is not proof that the person or company exists. The numbers travel in the request URL, so take care wherever you log URLs.