How to validate an IBAN's checksum

1. Enter the IBAN

   Paste the IBAN into the "IBAN" field. Spaces are stripped and letters are uppercased, so `de89 3704 0044 0532 0130 00` parses identically to `DE89370400440532013000`.

2. Press Run

   Result returns `length` (post-cleanup) and `checksumValid` (boolean). The mod-97 checksum (per ISO 13616): move first four chars to the end, replace letters A=10…Z=35, the resulting number mod 97 must equal 1.

3. What checksumValid doesn't prove

   A valid checksum does NOT prove the account exists, that the bank code is currently active, or that the IBAN belongs to the named beneficiary. For SEPA payments your bank still validates further server-side.

4. Country length hints

   DE is 22 chars, FR 27, IT 27, GB 22, NL 18, ES 24, SA 24, AE 23. Wrong length for the leading 2-letter country code is a strong typo signal even before checksum runs.