Card Number Validator

Check a payment card number the way a checkout form does: the Luhn checksum that every major network uses to catch a mistyped digit, and the scheme behind the prefix (Visa, Mastercard, Amex, Discover, JCB, Diners). It is a format check and nothing more: it says nothing about whether a card exists, is active or has funds. The number is never logged, stored or returned, and the result shows at most the last four digits.