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About Credit Card Luhn Validator Online
This tool validates credit card numbers using the Luhn algorithm — the checksum formula every major card brand (Visa, Mastercard, Amex, Discover) uses to catch typos. A number that passes Luhn isn't necessarily issued or active; it just has the right mathematical structure.
Luhn validation catches simple typing mistakes (single digit transcription errors, transposed digits) before sending the number to a payment processor. Catching these client-side saves bandwidth, reduces processor failures, and gives users better feedback than "declined".
This tool validates the checksum only — no network requests, no card processor lookups. Never paste a real card number into an untrusted online tool. For testing payment flows, use sandbox card numbers provided by Stripe, Adyen, or your processor.
How to use this tool
How to validate a card number with the Luhn check
Enter the card number
Paste the digits into the "Card number" field. Spaces and dashes are stripped, so `4111 1111 1111 1111` and `4111-1111-1111-1111` work the same as the bare digit string.
Press Run
Result returns `digitsLen` (digit count after stripping) and `luhnValid` (boolean). The Luhn pass means the checksum is internally consistent — NOT that the card exists at any bank.
What it doesn't tell you
Luhn doesn't verify the issuer, the cardholder, expiry, CVV, or available balance. Many test numbers (4242…, 5555…) pass Luhn but are sandbox-only. Don't use this for fraud screening.
Quick examples that should pass
Visa test: `4111111111111111` (16 digits). Mastercard test: `5555555555554444`. Amex test: `378282246310005` (15 digits). All three are well-known sandbox numbers.