Belgium sits at the short end of the IBAN spectrum: a BE test IBAN is just 16 characters. The structure is BE, two ISO mod-97 check digits, then a 12-digit BBAN made of a 3-digit bank code, a 7-digit account number and a 2-digit national check number. That final pair is Belgium’s own integrity layer, inherited from the pre-IBAN domestic format: the first ten BBAN digits modulo 97 must equal the last two (with 97 standing in for a remainder of zero).
Double mod-97, easy to conflate
Belgium is the country where developers most often confuse the two checksums, because both happen to be mod-97 based. They are computed differently and protect different substrings: the national check covers the 10-digit bank-plus-account body, while the ISO check digits after BE cover the whole rearranged IBAN. A fixture that satisfies one but not the other is a classic source of flaky “works with library A, fails with library B” reports. Values from this generator satisfy both, so your unit tests and your PSP sandbox agree.
Short IBANs find different bugs
Just as Poland’s 28 characters expose truncation bugs, Belgium’s 16 expose the opposite failure mode: minimum-length assumptions, padding logic that expects longer BBANs, and display groupers hardcoded for five or six blocks of four. A multi-country SEPA product should always keep a Belgian value in its fixture set as the short-end sentinel. Drop one into your form-validation unit tests and your end-to-end signup flow and both boundaries of the length range are covered.
The generator runs entirely in the browser, sends nothing over the network, and labels each output TEST so synthetic data cannot be mistaken for a customer record.
Testing only, and why that is enforced anyway
No generated Belgian IBAN corresponds to an account at any bank. Beyond the ethics, the EU’s Verification of Payee regime means banks now check that the recipient name matches the IBAN before executing euro credit transfers, so fabricated details fail operationally too. Use these values in test suites, sandboxes, demos and docs, never in real payment contexts.