This is a development tool for those in the payment industry and anyone interested in using it. It does not store or send your credit card number anywhere. It uses the MOD 10 check to determine if the card CAN BE a valid number or not based on the mathematical formula used by the MOD 10 check. If the card number passes the MOD 10 check, the application goes further and displays a large image indicating the card type associated with the number (amex, visa, mastercard or discover).
If you do not feel safe using yours, you can use these test card numbers: