Check if a card number passes the Luhn algorithm.
Credit Card Validator is a small tool that does one job while you watch. Nothing is saved, so a reload gives you a clean start.
Everything after the first page load is local. Pull the network cable mid-edit and the tool carries on as though nothing happened.
You will find it under Validators, alongside 17 other tools for the same sort of job.
Detects card type (Visa, Mastercard, Amex, Discover) and masks the number for display.
4111 1111 1111 1111
Valid card number Type: Visa Masked: 4111 **** **** 1111
1234567890123456
Invalid card number: Luhn check failed
Yes. It is JavaScript running in this tab, so once the page has loaded it needs nothing further from the network. Put the machine in flight mode and it carries on. Nothing you do here is sent anywhere, because there is nowhere for it to go.
No. Reload the page and it starts from nothing. There is no account, no saved state and no cookie holding your last session. That is a deliberate trade: it cannot lose your data because it never keeps any.
Timing comes from performance.now(), the high resolution clock the browser provides, rather than from setInterval, which drifts by a few milliseconds every tick and compounds over minutes. What can still shift things is the browser throttling a tab in the background, so leave it visible if the timing matters.
Where a sound makes sense, it is generated with the Web Audio API rather than loaded as a file, so there is nothing to download and nothing to block. Browsers refuse to start audio until you have interacted with the page, which is why the first press is what switches it on.
Yes. The controls are sized for touch and the layout collapses to one column on a narrow screen. Bear in mind that a phone locking its screen will suspend the page, and timing stops with it.