What Luhn does
Luhn applies a simple checksum calculation to digits. It can catch many common typing mistakes before a number is used in a test form, example, or format check.
What it does not do
A Luhn pass does not prove a card exists, is active, belongs to anyone, can be charged, or is accepted by a payment network.
Common mistakes
Do not enter real card security codes or financial credentials into format-check tools. Prefer test numbers for demos and development.
FAQ
Can a fake number pass Luhn?
Yes. Passing the checksum only proves the digit pattern matches the rule.
Is Luhn useful?
Yes, for catching many input mistakes in non-sensitive format checks.