What is the Luhn algorithm?

The Luhn algorithm is a checksum validation used by all major card networks to catch input errors. It validates the mathematical structure of a card number but does not verify the account exists.

Is my card number sent anywhere?

No. Validation runs entirely in your browser. Nothing is transmitted.

Which card networks are detected?

Visa, Mastercard, American Express, Discover, JCB, UnionPay, and Diners Club are identified from the card number prefix.

Best Free Credit Card Validator Online

Validating credit card numbers before a payment API call improves user experience by catching typos instantly and avoids wasted requests to payment processors. devtoolkit.sh's Credit Card Validator checks any card number using the Luhn algorithm and identifies the card network — Visa, Mastercard, Amex, Discover, and others — from the number prefix. All validation runs in your browser with zero server requests, making it safe to use during development with real card numbers. This is the fastest free way to test payment form validation logic, verify test card numbers, or check whether a manually entered number has the correct structure.

FAQ

What is the Luhn algorithm?: The Luhn algorithm is a checksum validation used by all major card networks to catch input errors. It validates the mathematical structure of a card number but does not verify the account exists.
Is my card number sent anywhere?: No. Validation runs entirely in your browser. Nothing is transmitted.
Which card networks are detected?: Visa, Mastercard, American Express, Discover, JCB, UnionPay, and Diners Club are identified from the card number prefix.