How credit card validator works
This validator runs two checks on a card number. First it identifies the issuing network from the BIN — the first few digits — using the published IIN ranges: Visa starts with 4, Mastercard with 51-55 or 2221-2720, American Express with 34 or 37, Discover with 6011, 65 or the 622126-622925 range, and so on.
Then it applies the Luhn checksum: starting from the rightmost digit, every second digit is doubled and, if the result exceeds 9, 9 is subtracted; the sum of all digits must be a multiple of 10. A number is valid only when it passes Luhn AND its length matches the identified network (for example 16 digits for Mastercard, 15 for Amex).
The tool validates only. It never stores, transmits, or logs the number — every check runs in your browser, so it is safe to paste a real card. It cannot tell you whether an account is open, has funds, or is authorised; it only confirms the number is structurally well-formed. Use it to catch typos in forms or to test payment-form input validation.