What is the Luhn algorithm?

A simple mod-10 checksum that doubles every second digit from the right and checks that the total is divisible by 10.

Should I paste a real card number?

No. Use published test numbers only — the tool is for developers validating formats, not for handling live card data.

Does passing Luhn mean the card works?

No. It only proves the number is well formed; authorisation still depends on the issuing bank.

Is my data uploaded to a server?

No. This tool runs entirely in your browser using standard web APIs, so your input never leaves your device and nothing is logged or stored on our servers.

Does it work offline and on mobile?

Yes. Once the page has loaded it keeps working without a network connection, and the layout is responsive so it stays usable on phones and tablets.

Credit Card Validator (Luhn)

Check card numbers with the Luhn algorithm and detect the brand.

Works Offline

Privacy First

No Login

No API

Card numbers

One number per line — use test numbers only, never a real card

Everything is checked locally in your browser. Numbers are never sent anywhere, but you should still only paste test data.

Results

Luhn checksum, brand detection and length rules

Valid

Invalid

Valid••••••••••••4242Visa
16 digits · Luhn passed · length allowed · CVV 3 digits
Valid••••••••••••4444Mastercard
16 digits · Luhn passed · length allowed · CVV 3 digits
Valid•••••••••••0005American Express
15 digits · Luhn passed · length allowed · CVV 4 digits
Invalid••••••••••••4241Visa
16 digits · Luhn failed · length allowed · CVV 3 digits

About the Credit Card Validator (Luhn)

Validate test card numbers with the Luhn (mod-10) checksum, detect the issuing network from the IIN prefix, and confirm the digit length and expected CVV size. Numbers are masked in the output and never leave your browser.

Examples

Visa test number

4242 4242 4242 4242

Output

Valid — Visa, 16 digits, Luhn passed

Keyboard shortcuts

Copy the main outputCtrl / ⌘ + Shift + C
Download the resultCtrl / ⌘ + S
Share this toolCtrl / ⌘ + Shift + S
Reset the inputsAlt + R
Open the tool search paletteCtrl / ⌘ + K

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Frequently asked questions

Version 1.0.0 · Updated 2026-08-17 · Runs entirely in your browser