How the keyboard tester works
Every key press your browser receives carries two names: its code, which says where the key sits on the keyboard, and its key, which says what it types on your layout. The tester lights keys up by code, so a French AZERTY keyboard lights the same physical keys as a US one. In Chrome and Edge it also relabels the letters and symbols to match your layout.
A key turns amber while it is held down and stays green once it has registered. Pick the layout and size that match your keyboard, press each key once, and the summary lists any that never arrived. A key that stays grey after a firm press is either faulty or intercepted before the page could see it.
The event log shows the raw events: each press and release, the key it typed, whether it was a repeat, which modifiers were held and how long after the previous event it came. Times come from the browser's own event timestamps, so a busy page doesn't blur them.
Rollover and ghosting
Rollover is how many keys a keyboard can report at the same time. Hold keys down one after another and watch the most-at-once count: it stops rising at your keyboard's limit.
- Many keyboards report 6 keys plus the modifiers (Ctrl, Shift, Alt and the Windows or Command key). That is the USB boot protocol, which every computer understands, and it is plenty for typing.
- Keyboards with n-key rollover (NKRO) report every key, however many are held.
- Cheaper membrane keyboards and many laptops share wiring between keys. Some three-key combinations would register a fourth key that nobody pressed, a ghost, so the keyboard blocks the combination instead and one of the keys goes missing.
The gaming combinations check the key groups games ask for. If one never registers in full while you are sure you are holding every key, your keyboard blocks that combination. Whether it matters depends on whether your games use it.
Key repeat
Hold a key down and your operating system waits a moment, then types it again and again. The tester measures the wait (the repeat delay) and the pace (the repeat rate, from the median gap between repeats). Both are settings of your operating system, not of the keyboard: on Windows under Keyboard in Control Panel, on a Mac under Keyboard in System Settings.
Double presses
A worn or dirty switch can bounce, so one press registers as two. When a key registers a new press less than 30 ms after being released, faster than a finger can manage, the summary points it out. Press that key slowly a few times to confirm.
What a browser can't see
Some keys never reach a web page, and the tester says so rather than marking them broken. Fn changes what other keys send inside the keyboard and is never sent to the computer. Media, brightness and backlight keys are often handled by the keyboard or the operating system, and power and sleep keys always are.
The operating system also keeps some presses for itself. Windows often keeps Print Screen and sometimes the Windows key, so only their release reaches the page: the tester marks those keys as detected on release. On a Mac, releases of other keys don't arrive while Command is held, so everything held is let go when Command comes up. And shortcuts such as Ctrl+W, Alt+Tab or Cmd+Q act before any page sees them.
In Chrome, Edge and Opera on a computer, fullscreen with system key capture uses the Keyboard Lock API to let Escape, the Windows or Command key and most system shortcuts through to the page. Hold Esc to leave fullscreen.
Questions
Why doesn't a key light up when I press it?
First make sure testing is on: the status next to the buttons says Capturing keys. If one key stays grey after firm presses while its neighbours work, the switch or its contact is likely faulty. Some keys can't light up by design: Fn never leaves the keyboard, and media, brightness and power keys are often handled before the browser. Keys your operating system keeps for itself, such as Print Screen on Windows, show up as detected on release only. If a key lights up somewhere else on the board, pick the layout that matches your keyboard.
What does n-key rollover (NKRO) mean?
Rollover is how many keys a keyboard can register at once. A keyboard with n-key rollover registers every key you hold, however many. Many keyboards stop at six keys plus modifiers, the limit of the basic USB keyboard protocol, which is more than typing ever needs. Hold keys down one by one and watch the most-at-once count: it stops at your keyboard's limit.
How do I test the Fn key?
Fn can't be tested directly, because it never reaches the computer: the keyboard uses it to change what other keys send. Test it through what it does instead. Hold Fn and press a key with a second function, such as F1 on a laptop or the number row on a 60% board, and check that the right key lights up here or appears under other keys detected.
Why do the Windows key and Print Screen behave oddly?
Windows handles some keys itself. Print Screen is often taken for screenshots, and the Windows key opens the Start menu, so only the release of those keys may reach the page. The tester marks such keys as detected on release: the key works, the system just got there first. In Chrome, Edge and Opera, fullscreen with system key capture lets more of these presses through.
What's the difference between ANSI and ISO keyboards?
They are the two common physical layouts. ANSI, used in the US, has a wide one-row Enter, a long left Shift and a backslash key above Enter. ISO, used across most of Europe, has a tall two-row Enter, a short left Shift with an extra key beside it, and one more key to the left of Enter. Letters on the keycaps are a separate matter: a German QWERTZ keyboard is ISO, and so is a UK QWERTY one.
Does the tester work with Mac keyboards?
Yes. On a Mac the modifier keys are labelled Cmd and Option, and a full-size Apple keyboard's extra F13 to F19 keys appear under other keys detected. Holding a letter on a Mac opens the accent menu instead of repeating it, so test key repeat with Space, an arrow or a digit. On some Mac ISO keyboards the browser reports the key left of 1 and the key beside left Shift swapped, so those two light up the wrong way round.
Is anything I type sent anywhere?
No. The tester runs entirely in your browser and keeps nothing: the keys you pressed, the log and the summary exist only on this page and are gone when you close or reload it.