Bulk VAT Validator uses regular expression matches to check if a vat number is formatted correctly for a given country, if the format looks good it then performs a check against the relevant authority (HMRC for UK VAT numbers and VIES for EU VAT numbers) to check the validity of the number. The user interface is very easy to use and we've made the process very simple so administrative staff can easily use the service.
VAT Numbers should be externally verified whenever you do business with a VAT registered customer or supplier, preferably before being entered into any accounting system. It is also recommended to perform additional checks on a regular basis, e.g. once per quarter.