Luhn Algorithm Checker
Check card numbers, IMEIs and other IDs with the Luhn (mod 10) algorithm, or calculate the check digit. Free and private: runs in your browser.
Paste numbers, one per line. Card numbers show only the first six and last four digits.
Numbers are checked locally in your browser and never sent anywhere. Use test data, not real customer details.
Use cases
- Validate test data for payment and banking flows.
- Catch typos in account and card details before calling a provider API.
- Explain money-handling rules to your team with real examples.
Frequently asked questions
What does the Luhn check catch?
Any single mistyped digit and most swaps of adjacent digits. It is a typo check, not a security check.
Is the Luhn Algorithm Checker free?
Yes. It is free with no sign-up, and it runs entirely in your browser, so your input is never uploaded or stored.
Can I use real customer data here?
Avoid it. Everything runs locally, but good practice (and PCI DSS) is to use test data outside production systems.
Related tools
Checking one snippet is a start. Scan your whole repository for free with CodeInspector.