Credit Card Luhn Checker & Masking

Validate card numbers with the Luhn algorithm, detect the brand, check in bulk, and mask card data — free and nothing stored.

Format check only. These tools run a public Luhn (mod-10) check and detect the brand from the number's prefix. No bank or payment network is contacted, and nothing you enter is stored. Passing Luhn only means the number is well-formed, not that a real, active card exists.

Luhn card check

Checks against Visa, Mastercard, Amex, Discover, Visa Electron, Diners Club, JCB, Maestro and UnionPay.

Card masking

Keeps the first and last 4 digits, replaces the middle with X (e.g. 4111XXXXXXXX1111).

Results

Results appear here after you check or mask a card.

Standard test card numbers

These are the publicly documented test numbers published by the card networks. They pass the Luhn check but are not linked to any real account — safe to use when testing software and payment forms.

BrandTest number
American Express371449635398431
Diners Club30569309025904
Discover6011111111111117
JCB3530111333300000
Mastercard5555555555554444
Visa4111111111111111

How many digits are in a card number?

  • Visa / Visa Electron: 13 or 16
  • Mastercard: 16
  • Discover: 16
  • American Express: 15
  • Diners Club: 14
  • Maestro: 12–19 (debit)
  • JCB: 15 or 16
  • UnionPay: 16–19

Frequently asked questions

What is the Luhn algorithm and how does this checker work?
The Luhn algorithm (the "mod 10" check) is a simple checksum used to validate identification numbers, most commonly card numbers. This tool doubles every second digit from the right, sums the digits, and confirms the total is divisible by 10. If it is, the number is format-valid — it does not mean the card exists or has funds.
Which card brands does the tool detect?
It recognises Visa, Visa Electron, Mastercard, American Express (Amex), Discover, JCB, Diners Club, Maestro and UnionPay using their published IIN/BIN prefix ranges (including the newer Mastercard 2221–2720 range). Anything else is reported as Unknown.
Does this tool store or send my card numbers anywhere?
No. The check runs only to compute the result for that request and nothing is saved to a database, log or third party. For real card data, prefer the built-in example and test numbers.
What is credit card masking and when should I use it?
Masking replaces the middle digits with X while keeping the first four and last four visible (for example 4111XXXXXXXX1111). It is used in receipts, logs and support tickets so a card can be referenced without exposing the full number, in line with PCI-DSS guidance.
Can I check many card numbers at once (bulk)?
Yes. Paste one number per line into the Bulk check box and each line is validated and brand-detected separately. The same works for bulk masking, and Export results downloads everything as a text file.
Are the example numbers real cards?
No. The example numbers (such as 4111 1111 1111 1111) are the standard, publicly documented test numbers published by the card networks. They pass Luhn but are not linked to any real account.
Why does a valid-looking number show as invalid?
Usually a typo or missing digit, extra characters, or a length outside the accepted 12–19 digits. The tool strips spaces and dashes automatically, so re-check the digits themselves.
Is using a card checker or masking tool legal?
Validating the format of card numbers and masking them for privacy are legitimate everyday tasks for developers, merchants and support teams. This tool performs offline mathematical checks only and never contacts any bank or payment network.