Online Tool Store
Credit Card Validator
Check a card number's Luhn checksum, detect its network, and validate its length — entirely in your browser, with nothing ever transmitted.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
Example shown — a well-known publicly documented test number. Nothing is sent anywhere; the check runs entirely on your device.
- Digits
- —
- Luhn check digit
- —
How it works
- Type or paste a card number — it's auto-formatted in groups of 4 digits.
- The network (Visa, Mastercard, Amex, etc.) is detected from its prefix.
- See instantly whether it passes the Luhn checksum and matches a valid length for that network.
The Luhn formula
Starting from the rightmost digit and moving left, every second digit is doubled (subtracting 9 if the result exceeds 9), then all digits are summed:
Sum of (doubled-every-other-digit, adjusted) must be divisible by 10
FAQ
Does "valid" mean the card is real and has funds on it?
No — this only checks that the number is mathematically well-formed (passes the Luhn checksum) and matches a known network's number-length pattern. Only the card issuer's payment network can confirm a card is real, active, and has available funds.
Is my card number sent anywhere?
No. The Luhn check is simple arithmetic run entirely in your browser — nothing is transmitted, logged, or stored, and there's no form to submit.
What's the Luhn algorithm actually checking?
It's a checksum formula built into how card numbers are generated — the last digit is chosen specifically so the whole number satisfies the formula. It catches most typos and transposed digits, but it doesn't know anything about whether the account actually exists.
Why does the example number stay in the field?
It's a widely published test number card networks provide specifically for development and testing — it will never charge or represent a real account.
How we compare
| Feature | Online Tool Store | Payment gateway test tools | Random online validators |
|---|---|---|---|
| No account or API key needed | ✓ | Developer account required | ✓ |
| No file upload — runs in your browser | ✓ | ✓ | Some send the number to a server |
| No ads | ✓ | ✓ | Ad-supported |
A number that never leaves your browser is the safer default for testing checkout form validation, even with a fake or test card number.