Credit Card Validator

The Luhn algorithm (Mod-10 checksum) validates card numbers by: 1) Starting from right, double every second digit, 2) If doubling results in two-digit number, add digits, 3) Sum all digits, 4) If sum is divisible by 10, checksum is valid. It detects most typing errors (single digit mistakes, adjacent digit transpositions) but cannot verify card activation, funds, or account validity.

No, generated test numbers are mathematically valid (pass Luhn) but are not tied to real accounts or payment methods. They're useful for testing validation logic and form behavior but cannot process real transactions. For payment testing, use test card numbers provided by your payment gateway (Stripe, PayPal) that simulate payment responses without charging real cards.

The validator supports Visa (starts with 4, 13-16 digits), Mastercard (starts with 51-55 or 2221-2720, 16 digits), American Express (starts with 34 or 37, 15 digits), Discover (starts with 6011, 65, or 622126-622925, 16 digits), Diners Club (starts with 300-305, 36, or 38, 14 digits), and JCB (starts with 2131, 1800, or 3528-3589, 16 digits) based on common BIN (Bank Identification Number) range patterns.

No, all validation happens entirely locally in your browser using client-side JavaScript. No card numbers, validation results, or any data is transmitted to external servers. This ensures complete privacy and security—however, remember this is a validation tool only and does not process payments or verify card activation.

Format validation checks card number structure (correct length, numeric characters only, matches network pattern). Luhn validation verifies the checksum digit using mathematical algorithm. Both checks are needed: format ensures structure, Luhn ensures checksum correctness. A number can have correct format but fail Luhn (typing error), or pass Luhn but have wrong format (wrong network).

Common reasons: wrong digit count (Amex needs 15, others need 16), incorrect BIN range (doesn't match detected network), failed Luhn checksum (typing error in digits), or non-numeric characters. Check network detection matches your card type, verify digit count, and ensure Luhn algorithm passes. If all checks pass but card still doesn't work, issue may be card activation, funds, or payment gateway authorization—validation only checks structure.

The validator performs format and Luhn checks on any numeric input, but network detection requires known BIN ranges. If your network isn't detected, validation still checks format and Luhn—network detection helps verify expected length and format. For unknown networks, verify length requirements manually and use Luhn validation results.

BIN range detection is generally accurate for major networks but can have edge cases: new BIN ranges, regional variations, or issuer-specific BINs may not match known patterns. Network detection helps validate expected format and length but isn't 100% exhaustive—some valid cards may not be detected if BIN isn't in the detection table.

Both: validate on client side for immediate user feedback and better UX (instant formatting, error detection), but always re-validate on server side for security (client validation can be bypassed). Client-side validation improves UX, server-side validation is essential security layer. Never rely solely on client-side validation for security.

If a card number you believe is correct fails Luhn, double-check: 1) Verify all digits entered correctly (common typing errors), 2) Check card number isn't missing or has extra digits, 3) Ensure correct network format. If number is definitely correct but fails Luhn, the card number itself may be invalid—contact card issuer. Luhn detects most errors, so failures usually indicate actual problems.

No, this validator only checks structural correctness (format, length, Luhn checksum). It cannot verify card activation, available funds, cardholder identity, expiration validity, or payment authorization. Those verifications require payment gateway authorization (Stripe, PayPal) with actual payment processing attempts. Use this validator for format/structure checks only.

Use generated test numbers from this tool for validation testing, or use test card numbers provided by your payment gateway (e.g., Stripe test cards like 4242 4242 4242 4242). Payment gateway test numbers simulate payment responses. Never use real card numbers for testing—always use test numbers in development/test environments, and ensure production systems reject test card numbers.