Bank Card Number Validator

📖 Tool Introduction

Bank Card Number Validator is a free online format-checking tool built on the Luhn algorithm, also known as the modulus 10 algorithm. Almost every bank card, credit card and debit card number in the world follows this public checksum rule: starting from the rightmost check digit and moving left, digits in odd positions are added directly, digits in even positions are doubled first, and if the product is greater than 9 then 9 is subtracted from it, which is equivalent to summing the two digits of the product. The final total is taken modulo 10, and a remainder of 0 means the number follows the encoding rules. This tool implements the algorithm entirely in your browser and adds card-network detection based on the BIN prefix, so it can tell whether a number belongs to Visa, Mastercard, China UnionPay, American Express, JCB, Diners Club or Discover. The interface is styled like a physical card: as you type, the number appears on the card image in groups of four digits, and the result is shown as a green or red status bar. Below the card there is a reference table of common card-network prefixes and standard lengths, which is handy when you are testing a payment form, debugging input validation, or learning how Luhn works. Everything runs offline, no card number is uploaded, and no bank system is contacted; the tool only checks the format and never verifies that a number belongs to a real account. Because it is purely local, you can safely enter test numbers such as the well-known Visa test number without worrying about anyone intercepting the input, and the instant visual feedback makes it easy to see how one typo in a digit flips the checksum from valid to invalid.

✨ Key Features

• Standard Luhn: implements the right-to-left doubling with subtract-9 rule exactly as specified
• Network detection: identifies Visa, Mastercard, UnionPay, Amex, JCB and more from the BIN prefix
• Card visual: the typed number appears on a simulated card image in four-digit groups
• Length hints: warns when the length is outside the common 13-19 digit range
• Prefix reference table: built-in table of common network prefixes and standard lengths
• Fully offline: all validation runs locally, no card number is ever uploaded

📝 How to Use

1. Type a card number into the input field (digits only, spaces and dashes are ignored)
2. The simulated card above updates in real time, showing your number in four-digit groups
3. Click Check number or press Enter to see the green or red result bar
4. The result shows the detected card network and the total number of digits
5. Use the prefix table below to cross-check the network detection

⚠️ Notes

• Format check is not existence: a passing Luhn check only means the number follows the rules, not that it belongs to a real account
• Privacy: this tool never contacts any bank system; do not enter your real card number for testing
• Prefix reference: the network table covers common public ranges; some special BINs may show as unknown
• Length range: mainstream card numbers are 13-19 digits; anything outside that range triggers a warning
• Learning use: this tool is intended for form development and Luhn education, and is not financial advice