About this tool
The IBAN Validator & Parser checks an International Bank Account Number for correctness and splits it into its parts — country, check digits, bank code, branch/sort code, and account number. It validates entirely offline in your browser (no bank lookup, no network), so it confirms structural and checksum validity, not whether the account actually exists.
Validation follows the ISO 13616 registry and the ISO 7064 MOD-97-10 algorithm. First the input is stripped of spaces and upper-cased, and its length is checked against the per-country table (for example DE=22, GB=22, FR=27, NL=18, ES=24; about 80 countries are bundled). Then the first four characters (country code plus the two check digits) are moved to the end, each letter is replaced by a number (A=10 … Z=35), and the resulting digit string is interpreted as a large integer; the IBAN is valid if and only if that integer mod 97 equals 1. The remainder is computed incrementally, digit by digit, so no big-number library is needed.
When the length and checksum pass, the BBAN is parsed using the country's structure table into bank code, branch, national check digits, and account number where those positions are known. A 'compute check digits' mode sets positions 3–4 to '00', runs the algorithm, and returns 98 − (mod 97) as the correct two check digits — useful when you have the country and BBAN and need to build the full IBAN. The result also shows the value formatted in the standard groups of four.