The first 6-8 digits of any payment card are the Bank Identification Number (BIN), also called the Issuer Identification Number (IIN). It is a public prefix that maps to a card network, so this checker can identify the scheme — Visa, Mastercard, American Express, Discover, JCB, Diners Club, UnionPay or Maestro — from just those leading digits, and run a Luhn check if a full number is supplied. You only ever need the BIN, not a full card number.
How it works
Card networks reserve known prefix ranges, so the tool matches the leading digits of the number against those ranges, ordered most-specific first so the first match wins:
| Network | Starts with | Length |
|---|---|---|
| Visa | 4 | 13, 16, 19 |
| Mastercard | 51-55, 2221-2720 | 16 |
| American Express | 34, 37 | 15 |
| Discover | 6011, 65, 644-649, 622 | 16 |
| Diners Club | 36, 38, 300-305 | 14 |
| JCB | 3528-3589 | 16 |
| UnionPay | 62 | 16-19 |
When you enter a full number it also runs the Luhn (mod-10) check to confirm the number is well-formed. The lookup is a local prefix table, so nothing is sent anywhere.
Example
A number beginning 4539 is identified as Visa (it starts with 4). A number beginning 5425 is Mastercard (51-55 range), and 3782 is American Express (34/37). The prefix alone reveals the network — it cannot reveal the cardholder, the bank account or whether the card is active. Everything runs in your browser with nothing uploaded.