Credit Card Validator

How card validation works

Every credit card number ends with a check digit computed by the Luhn algorithm: doubling every second digit from the right (subtracting 9 when the result exceeds 9) and confirming the total is divisible by 10. This catches most typos. The brand is inferred from the leading digits (Visa starts with 4, Amex with 34/37, and so on). Note that passing Luhn only means the number is well-formed — not that it's a real, active account. All checks run locally in your browser.