Credit Card Checker
Check whether a card number passes the Luhn checksum and identify its network - validated entirely in your browser, so the number is never sent anywhere.
Card number validator (Luhn check)
The number is checked locally with the Luhn algorithm - it is never sent, stored or logged anywhere. This verifies the checksum only; it cannot tell whether a card actually exists or has funds.
Handy for validating test numbers in payment integrations (e.g. 4111 1111 1111 1111). Never paste real card details into websites you do not fully trust - even this one.
About Credit Card Checker
Almost every payment card number carries a built-in checksum defined by the Luhn algorithm (also called the mod-10 check). Starting from the rightmost digit, every second digit is doubled - subtracting 9 when the result exceeds 9 - and all digits are summed; a number is well-formed only when that total is divisible by 10. This simple test catches the overwhelming majority of single-digit typos and adjacent transpositions, which is exactly why it guards card entry forms everywhere. This validator applies the algorithm to whatever you type, ignoring spaces and dashes.
It is important to understand what a passing result does and does not mean. A valid Luhn checksum confirms only that the digits are internally consistent. It says nothing about whether the card was ever issued, is active, or has available funds - those facts are known only to the issuer and are confirmed during an authorization. A randomly generated string can pass Luhn while corresponding to no real account.
Alongside the checksum, the tool identifies the likely network from the number's leading digits: Visa (starting with 4), Mastercard (the 51-55 and 2221-2720 ranges), American Express (34 and 37), Discover, Diners Club, JCB, and Maestro. It accepts numbers from 12 to 19 digits, covering the common 16-digit Visa and Mastercard formats, 15-digit American Express, and variable-length Maestro cards.
Validation happens locally in JavaScript, so the number is never transmitted, stored, or logged. That makes the checker well suited to verifying test card numbers - such as 4111 1111 1111 1111 - while building a payment integration. As a general habit, never paste a real card number into a website you do not fully trust, including this one; the safest number to test with is always a published test value.
How to use it
- 1Type or paste the card number into the field - spaces and dashes are accepted.
- 2The checker strips formatting and applies the Luhn algorithm as you type.
- 3Read the checksum verdict (valid or invalid) and the detected card network.
- 4Use it to sanity-check test card numbers while building a payment integration.
Common use cases
- -Developers verifying that test card numbers behave correctly in a gateway sandbox or checkout.
- -Catching a mistyped or transposed digit in a card number before a form is submitted.
- -Learning or teaching how the Luhn checksum and card-number structure work.
- -Identifying which network a card belongs to from its leading digits.
Frequently asked questions
- What is the Luhn algorithm?
- The Luhn algorithm, or mod-10 check, is a checksum that validates identification numbers such as credit cards. It doubles every second digit from the right, sums all the digits, and confirms the total is divisible by 10, catching most typos and single transpositions.
- Does passing the Luhn check mean a card is real?
- No. A valid Luhn check confirms only that the digits form a correct checksum. It does not prove the card was issued, is active, or has funds - that can only be confirmed by the issuer during an authorization.
- Is my card number sent to a server?
- No. The Credit Card Checker runs entirely in your browser. The number is validated locally on your device and is never transmitted, stored, or logged.
- How does it detect the card brand?
- It matches the leading digits against each network's published prefix ranges - numbers starting with 4 are Visa, 34 and 37 are American Express, and the 51-55 and 2221-2720 ranges are Mastercard. Detection uses the prefix, not an external lookup.
- How many digits should a credit card number have?
- Most card numbers are 13 to 19 digits; this tool accepts 12 to 19. Visa and Mastercard are usually 16 digits, American Express is 15, and Maestro cards vary in length.