Credit Card Number Validator
What is Credit Card Number Validator
This tool checks whether a credit or debit card number is structurally valid using the Luhn checksum algorithm, the same check payment processors run before a transaction ever reaches a bank. It also detects the card network from the number's prefix, Visa, Mastercard, American Express, Discover, Diners Club, JCB or UnionPay, and formats the digits into readable groups. Everything runs locally in your browser; no card number is ever sent to a server.
How to use
- Type or paste the card number into the field.
- Watch the digits get validated as you type.
- Check the Luhn checksum result and the detected card network.
- Copy the formatted number if you need it for a test form.
When to use it
Building a checkout form and need to confirm your test card number is actually valid before debugging a failed submission? Paste 4111111111111111 and you instantly see it's a Luhn-valid Visa test number, so if your form still rejects it, the bug is in your code, not the card. Handy for QA engineers testing payment flows, developers wiring up Stripe or PayPal sandboxes, or anyone who mistyped a digit and wants to know before submitting.
Frequently asked questions
Does this tool check if a card number is real or has funds?
No. It only verifies that the number is mathematically well-formed via the Luhn algorithm and matches the length and prefix of a known network. It can't tell you if the card exists, is active, or has any balance, that check only happens against the issuing bank.
What is the Luhn algorithm?
It's a simple checksum formula invented in 1954 that catches most typos and randomly generated numbers. Networks assign the last digit specifically so the full number passes this checksum, so almost every accidental slip of a digit fails the check.
Is it safe to paste a real card number here?
The check runs entirely in your browser and nothing is sent anywhere, but as a habit avoid pasting real card numbers into any web tool. Use one of the public test numbers instead, like 4111111111111111 for Visa or 5555555555554444 for Mastercard.
Why does the tool say the network is unknown?
Every card network reserves a specific range of starting digits, for example 4 for Visa or 34/37 for American Express. If the number doesn't match any known prefix, or has the wrong length for its network, it shows as unknown even when the Luhn check itself passes.
Related tools
Fake Credit Card Number Generator
Generate random, Luhn-valid fake credit card numbers for Visa, Mastercard, Amex and Discover to test payment forms safely.
Aspect Ratio Calculator
Calculate aspect ratios, find a missing width or height, and resize images or video while keeping the same proportions. Free and instant.
Base64 Decoder
Decode Base64 strings to plain text instantly in your browser. Supports full Unicode output including emojis. Free online Base64 decoder.