Luhn algorithm validator

How it works

The Luhn algorithm is a simple checksum used to detect typing errors in numbers such as credit cards, phone IMEI numbers or certain national identifiers. It doubles every second digit starting from the right, adjusts values greater than 9, then checks that the total sum is a multiple of 10. It's a handy way to quickly confirm that a manually entered number has no obvious typo before submitting it to a real payment system.

Is a number that is "valid" according to Luhn necessarily a real card number?

No. The Luhn check only detects common typing errors (a wrong digit, two adjacent digits swapped); it doesn't guarantee that the number actually exists or is linked to an active account. Only a check with the issuer or the payment network can confirm that.

What types of numbers use the Luhn algorithm?

It's found in credit card numbers (Visa, Mastercard...), mobile device IMEI numbers, IBAN numbers in some countries, as well as various national or business identifiers depending on the country.

100% local processing: the check runs entirely in your browser via WebAssembly, and the number you enter is never sent to a server.