Luhn Validator
Paste a card, IMEI, or any number and check it against the Luhn algorithm. Runs entirely in your browser — nothing is uploaded.
Luhn check in your browser
Paste a number — a credit/debit card, an IMEI, or any identifier that uses a Luhn (mod-10) check digit — and instantly see whether it's valid. Everything runs locally in your browser; the number is never uploaded.
What you get
- Valid / invalid against the Luhn algorithm.
- The correct last (check) digit if it's invalid — handy for catching a single-digit typo or completing a number.
- A best-effort card brand (Visa, Mastercard, Amex, Discover, JCB, Diners) when the length and prefix match.
Notes
- Spaces and dashes are ignored, so you can paste
4242 4242 4242 4242. - The Luhn check catches most accidental typos, but passing it does not mean a card is real or active — it's only a checksum.
FAQ
If a number passes, does that mean the card is real?
No. Luhn is only a mod-10 checksum designed to catch typos — every issued card passes it, but so do infinitely many made-up numbers. Whether an account exists, is active, or has funds can only be verified by the card network, which this tool never contacts.
What is the "expected check digit" it reports?
It's the last digit that would make your number pass the Luhn check. If a number comes back invalid, comparing its actual last digit with the expected one often pinpoints a single-digit typo — and if you're constructing a test number, it tells you which final digit to append.
Which characters are allowed in the input?
Digits, spaces, and dashes only — so 4242 4242 4242 4242 and
4242-4242-4242-4242 both work. Any other character stops the check with an
error naming it, and at least 2 digits are required.
Why doesn't it show a card brand for my number?
Brand detection is best-effort: it only reports Visa, Mastercard, Amex, Discover, JCB, or Diners when both the prefix and length match that scheme. IMEIs and other Luhn-checked identifiers aren't cards, so they validate fine but show no brand.
Developer & Automation Access
Run it from the terminal
Same engine as this page, headless — via the gizza CLI:
gizza tool luhn-validate "4242 4242 4242 4242"New to the CLI? Get gizza →
Open it by URL
Pre-fill and auto-run this tool with query parameters — the names match the API/CLI:
https://gizza.ai/tools/luhn-validate/?number=4242%204242%204242%204242Machine-readable descriptor: tool.json — title + parameters JSON Schema for agents.