Test Card Number Generator (Luhn-Valid, Sandbox Only)

This tool generates fake, synthetic card numbers for one purpose only: exercising a checkout form, a payment SDK integration, or an automated test suite without touching a real account. It is not a way to obtain a working card, and none of its output is tied to any real account, cardholder, or bank. Every number is built on top of a BIN prefix that payment processors publish in their own developer-facing sandbox documentation specifically so engineers can fill in test-mode payment forms - the exact same 424242..., 411111..., 555555..., 510510..., 378282..., 371449..., and 601111... style prefixes referenced across mainstream gateway test-mode docs. Nothing here works for a real purchase, in a real store, on a real payment network.

What makes the output valid-looking rather than just a random string is a real Luhn (mod-10) checksum, computed from scratch on every generation: starting from the rightmost digit of the candidate number, every second digit is doubled, any doubled result over 9 has 9 subtracted from it, all digits are summed, and the one remaining digit is chosen so the grand total lands on a multiple of ten. That is the same arithmetic a browser-side "looks like a valid card number" check performs, so these numbers pass that specific, narrow test the same way a real card number would - while still being entirely fake, generated locally, and useless for an actual transaction.

The tool keeps the documented test prefix fixed per network and randomizes everything after it, so a batch of up to 20 numbers is genuinely 20 different valid-Luhn numbers rather than the same well-known literal test number printed repeatedly. Each result is then re-classified by the real BIN-range rules payment forms use to detect a card's network (a leading 4 for Visa, 51 through 55 or 2221 through 2720 for Mastercard, 34 or 37 for Amex, 6011 or 65 for Discover) purely to confirm the label shown matches the digits generated, plus a correctly-sized CVV (3 digits, or 4 for Amex) and an optional random future expiry date for convenience when filling in a full test form.

This is a developer and QA convenience, not a payment product: it exists because Stripe, PayPal, and most other processors already publish these exact test-only numbers for anyone integrating their checkout, and having a quick way to generate variations that still satisfy client-side Luhn validation saves re-typing the same few textbook numbers by hand. Everything runs locally in your browser with Web Crypto-backed randomness - nothing is transmitted anywhere, and nothing produced here should ever be entered into a real merchant's live checkout.