Modulus Checker is software developed by Ardbrook Limited, that enables the user to validate the accuracy of any sort code / bank account number combination, for the clearing banks within the Republic of Ireland and Northern Ireland; and sort code only for the non-clearing banks.

This is achieved by running in reverse the internal algorithms of each of the clearing banks on the sort code / bank account numbered entered. Modulus Checker contains a complete user-maintainable database of all bank branches within the Republic of Ireland and Northern Ireland.

There are two DLL versions available, .NET or Active X. As a DLL, it allows the user to call the validation routines within Modulus Checker directly from within their own software. This necessitates a software change to be made to in-house systems to allow for immediate validation, on the input of a sort code bank account number combination through an automatic call being made to the DLL. Then a pass or fail verdict is returned to the user.