Run the Luhn check, see the card brand and the digit count a number should have, and list public test numbers.
To validate a credit card number, enter it and the tool runs the Luhn check, finds the card brand from the first digits and checks that the length fits that brand. Passing means the number is well formed. It does not mean the card exists, is active or has funds, and the tool does not look at an expiry date or a security code. Spaces and dashes are ignored, and a number must have 10 to 19 digits. Use test numbers here. The numbers are checked in your browser and are not stored or sent anywhere, but a form does not need your real card to be tested.
Start at the last digit, which is the check digit, and move left. Leave that digit as it is, double the next one, leave the next, double the next, and so on. If a doubled digit is over 9, subtract 9. Add everything up. The number passes if the sum is a multiple of 10. For 4242 4242 4242 4242 the eight 2s that are not doubled add up to 16, the eight 4s that are doubled become 8 each and add up to 64, and 16 + 64 = 80, so it passes. Change the last digit to 3 and the sum is 81, so it fails; the tool then shows 2 as the last digit that would pass. Luhn catches every single-digit mistake and nearly every swap of two neighbouring digits. The only swap it misses is 09 for 90.
The first digits, the issuer identification number, show the network. The tool uses the longest matching range. Visa: starts with 4, 13, 16 or 19 digits. Mastercard: 51 to 55 or 2221 to 2720, 16 digits. American Express: 34 or 37, 15 digits. Discover: 6011, 644 to 649, 65 or 622126 to 622925, 16 to 19 digits. Diners Club: 30, 36, 38 or 39, 14 to 19 digits. JCB: 3528 to 3589, 16 to 19 digits. UnionPay: 62, 16 to 19 digits. Maestro, Mir and Dankort ranges are included too. A number that matches a brand but has another length is reported as such. The ranges follow the public table on Wikipedia's Payment card number page, fetched on 15 October 2026, and networks add ranges over time, so an unrecognized brand is not proof that a number is wrong. Numbers are shown in groups of four; American Express is 4-6-5.
Turn on Also list public test numbers for 14 numbers taken from the test cards that Stripe publishes in its documentation, such as 4242 4242 4242 4242 for Visa, 5555 5555 5555 4444 for Mastercard and 3782 822463 10005 for American Express. All of them pass this check. Paste several numbers, one per line, to check up to 200 at once; the table shows each result. The text box accepts up to 20,000 characters. The work happens in your browser; nothing is uploaded or stored, only your option choice is remembered.
Paste it in the box. The tool removes spaces and dashes, runs the Luhn check, finds the brand and tests the length. A Visa with 16 digits that sums to a multiple of 10 shows Passes Luhn and the length rule. That only means the number is well formed.
A check-digit formula. From the right, double every second digit, subtract 9 from any result over 9, add all the digits, and the total must end in 0. The last digit of a card number is chosen to make that true. It finds typing mistakes; it is not security.
Usually one digit is wrong or two were swapped. The tool shows the last digit that would make the number pass, for example 2 instead of 3 for 4242 4242 4242 4243. If you typed the number from a card, check each group of four against it.
By the first digits. 4 is Visa, 51 to 55 and 2221 to 2720 are Mastercard, 34 and 37 are American Express, 6011 and 65 are Discover, 3528 to 3589 is JCB and 62 is UnionPay. The tool also checks that the length fits, such as 15 digits for American Express.
Use numbers that payment providers publish for tests. Stripe lists 4242 4242 4242 4242 (Visa), 5555 5555 5555 4444 (Mastercard) and 6011 1111 1111 1117 (Discover); turn on Also list public test numbers to see 14 of them. They are not real cards.
No. The text is processed in your browser, in this tab, and no server receives it. Only your option choice is saved in this browser; the numbers are not.