BYTETOOLS

Credit Card Validator

Validate a credit card number with the Luhn algorithm and detect the brand (Visa, Mastercard, Amex, Discover and more) locally. Numbers are never sent anywhere.

Numbers are validated locally in your browser and are never sent, logged or stored anywhere. This checks format and the Luhn checksum only — it cannot tell whether a card is real or active.

  • Luhn algorithm checksum validation
  • Brand detection by IIN range
  • Recognises Visa, Mastercard, Amex, Discover and more
  • Formats the number into readable groups
  • Step-by-step Luhn explanation
  • 100% private — numbers are never sent anywhere

How to use the Credit Card Validator

  1. 1

    Type or paste the card number, with or without spaces.

  2. 2

    Read whether it passes the Luhn checksum.

  3. 3

    See the detected card brand from its leading digits.

  4. 4

    Check the formatted number grouped for readability.

  5. 5

    Review the Luhn working to understand the checksum.

About the Credit Card Validator

The ByteTools Credit Card Validator checks whether a card number is well-formed using the Luhn algorithm, the checksum every real card number satisfies. It also identifies the brand — Visa, Mastercard, American Express, Discover and others — from the issuer identification number (the leading digits) and formats the number into readable groups.

It is built for developers testing payment forms, QA engineers checking validation logic and anyone verifying that a typed number has no digit errors. The tool explains how the Luhn checksum works step by step, so it doubles as a learning aid.

Every check runs entirely in your browser with JavaScript. Card numbers are validated locally and are never sent, logged or stored anywhere. This is a format and checksum check only — it does not and cannot tell you whether a card is real, active or has funds.

Frequently asked questions

What does the Luhn algorithm check?

The Luhn algorithm is a checksum that catches most single-digit typos and simple transpositions in a card number. Every valid card number satisfies it, so a number that fails Luhn is definitely mistyped, though passing does not mean the card exists.

How is the card brand detected?

The brand is identified from the issuer identification number — the first few digits. Visa starts with 4, Mastercard falls in specific 51–55 and 2221–2720 ranges, American Express starts with 34 or 37, and so on. The tool matches these ranges.

Does a valid result mean the card is real?

No. This tool only checks the number's format and Luhn checksum. It cannot tell whether a card was ever issued, is active or has available funds — only the issuing bank's systems can confirm that during an actual transaction.

Is it safe to enter a real card number?

The number is validated entirely in your browser and is never transmitted, logged or stored. That said, for a pure format check you can use published test numbers; there is no need to enter a live card to see how the tool works.

Why does my valid card fail the check?

Almost always it is a typo — a missed or swapped digit. Re-enter the number carefully, without extra characters. If it still fails Luhn, double-check each digit against the physical card, as the checksum is very reliable at catching errors.

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