Keyboard Tester
Click anywhere on this page, then start pressing keys. Keys light up green once they've been verified.
How to test rollover and ghosting
Hold down as many keys as you can at once and watch the Max simultaneous counter. A keyboard with N-key rollover (NKRO) registers every key you hold; cheaper boards stop at 6 (common over USB) or even 2–3 in some key regions.
Ghosting is when a key you never pressed registers because of the keys you did press. If a key lights up that you didn't touch, that combination ghosts on your board.
Keys are matched by physical position (event.code), so this works with any layout — QWERTY, AZERTY, Dvorak, or non-US layouts.
A key isn't registering — is it broken?
First rule out software: some keys (media keys, Fn, certain laptop specials) are handled by the OS or firmware and never reach the browser. Fn in particular is invisible to any keyboard tester. If a normal letter/number key doesn't register here but works in other apps, try another browser; if it fails everywhere, the switch or membrane under that key is likely faulty — on mechanical boards a switch swap or a contact clean usually fixes it.
What rollover numbers actually mean
Rollover is how many keys your keyboard can report at the same time. Office membrane boards typically manage 2–6 keys, and which combinations work depends on the wiring matrix — that's why some three-key game combos fail while others are fine. 6KRO (six keys plus modifiers) is the classic USB limit and enough for almost everyone. NKRO — every key at once — matters for rhythm games, stenography and fast gaming combos. If the counter above stops at 6 while you hold more, your board is running in 6KRO mode; some mechanical keyboards ship that way for compatibility and enable NKRO with a hotkey (check the manual — often Fn+N).
A key that types twice: switch chatter
If one press sometimes produces two characters ("chatter"), the switch contacts are bouncing faster than the firmware's debounce window. On mechanical boards this is a known wear symptom — fixes, in order: blow out the switch with compressed air, a drop of contact cleaner into the switch stem while working the key, a firmware update if the vendor offers one (some let you raise the debounce time), and finally a switch swap — on hot-swap boards that's a two-minute job with no soldering.
Testing a laptop keyboard
Everything here works for laptop keyboards too, with two caveats: the Fn layer is handled entirely in hardware and never reaches the browser, and shortcut combos the OS reserves (like Cmd+Tab or Win+L) will switch apps instead of registering. If several neighboring laptop keys die at once — especially after a spill — it's usually one membrane trace, and the fix is a keyboard deck replacement rather than a single key.