Sometimes people make mistakes when entering credit card numbers in web forms, or even just make numbers up to see what will happen. Using this plug-in you can at least ensure that a credit card number and expiration date you have been provided with has an acceptable number sequence, a correct checksum and a valid expiry date. This enables you to only pass on sensible-looking details to your card processing organization, and possibly limit any additional fees that may be charged.

The Figure shows a made up credit card number that doesn't pass validation.

Credit Card numbers have a built-in checksum which this plug-in will validate