A credit card validator checks whether a card number passes the Luhn algorithm (mod 10 check digit), detects the card network by prefix, and verifies the number length is valid for that network. Used by developers to test payment forms, validate test data, and verify card number generation logic.
FOR TESTING ONLY. Never enter a real credit card number. This tool validates format only — it cannot be used to process payments. All validation runs locally in your browser.
Validation Checks
Card Details
Generate Test Numbers
Create Luhn-valid test numbers for each card network. These are NOT real card numbers.
Card Network Prefix Reference
| Network | Prefix(es) | Length(s) |
|---|---|---|
| Visa | 4 | 13, 16, 19 |
| Mastercard | 51–55, 2221–2720 | 16 |
| Amex | 34, 37 | 15 |
| Discover | 6011, 622126–622925, 644–649, 65 | 16, 19 |
| Diners Club | 300–305, 36, 38 | 14 |
| JCB | 3528–3589 | 16 |
How to Use the Credit Card Validator
A credit card validator uses the Luhn algorithm to verify the mathematical integrity of a card number, and checks the prefix and length against known card network ranges. This is useful for developers testing payment flows, QA engineers validating form inputs, and anyone building systems that accept card data.
How the Luhn Algorithm Works
The Luhn algorithm (also called "mod 10") is a simple checksum formula designed to catch common typos. Starting from the rightmost digit (the check digit) and moving left, double every second digit. If doubling produces a number greater than 9, subtract 9. Sum all the digits — if the total is divisible by 10, the number passes the Luhn check. For a 16-digit Visa card like 4532015112830366, this sum must equal a multiple of 10.
Entering a Card Number for Testing
Type or paste a card number into the input field. The tool automatically formats it with spaces every 4 digits for readability (Amex uses 4-6-5 grouping). Validation runs automatically as you type. The checklist shows four checks: digit-only input, valid length for the detected network, recognized card network prefix, and Luhn check digit.
Generating Test Card Numbers
Use the "Generate Test Number" buttons to create valid test numbers for Visa, Mastercard, Amex, or Discover. These numbers are mathematically valid (they pass Luhn and have the correct prefix) but are NOT real card numbers and cannot be used for transactions. They are suitable for testing payment form validation, API integrations, and card number parsing logic.
Understanding the Results
A card that passes all four checks is "valid format" — meaning it could theoretically be a real card number of that type. However, format validity does NOT mean the card is issued, has available credit, or belongs to anyone. Real payment authorization requires the card issuer's systems, expiry date, and CVV. Use this tool for development and testing only.
FAQ
What is Luhn algorithm validation?
The Luhn algorithm (also called mod 10) is a simple checksum formula used to validate credit card numbers, IMEI numbers, and other identification codes. It works by doubling every second digit from the right, summing all digits, and checking if the total is divisible by 10. Major card networks including Visa, Mastercard, American Express, and Discover all use Luhn-compliant card numbers.
Should I enter my real credit card number?
No. This tool is designed for testing and development purposes only. Never enter a real credit card number — even though all processing happens locally in your browser, it is good security practice to never type real card numbers into any web tool. Use the 'Generate Test Number' feature to create valid test numbers for each card network.
Why would a number pass Luhn but still be invalid?
The Luhn check only verifies the mathematical format — it cannot check if a card number is actually issued, active, or belongs to a real account. A number that passes Luhn has the correct check digit structure but may not correspond to any real card. Real card validation also requires expiry date, CVV, and bank authorization — all of which require the card issuer's systems.
How does card network detection work?
Each card network reserves specific number prefixes (called Bank Identification Numbers or BINs). Visa cards start with 4, Mastercard starts with 51-55 or 2221-2720, American Express starts with 34 or 37, and Discover starts with 6011 or 65. This tool checks the prefix against known ranges to identify the likely issuing network.
Are the generated test numbers real card numbers?
No. The generated test numbers are mathematically valid (they pass the Luhn check and have the correct prefix for the selected network) but they are not real card numbers and cannot be used for actual transactions. They are suitable for testing payment forms, APIs, and validation logic.
Is this tool free?
Yes, completely free. No account or signup required. The Luhn check and all validation run in your browser.