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Device test · Input

Keyboard Tester

Press any key. It lights up the moment your keyboard reports it — no download, nothing leaves your browser. Use it to find dead keys, catch double-typing switches, and check how many keys register at once.

Key— Code— Held0 Max rollover0 Tested0 Capsoff

How this test works

Every physical key press generates a keydown event that your operating system passes to the browser. This page listens for those events and lights the matching key. Two properties matter: code identifies the physical position of the key regardless of language layout, and key is the character or action your layout actually produced. The tester maps by code, which is why an AZERTY "A" correctly lights the key in the Q position — same switch, different legend — while the readout shows the character your layout typed.

The rollover counter tracks how many keys are held simultaneously and records the maximum. Keyboards on basic membrane controllers usually guarantee 6-key rollover plus modifiers; some drop specific three-key combinations entirely, which is called ghosting. If a combination won't register no matter how you press it, that's the controller's wiring matrix, not the switches.

A few keys can't be tested from a web page by design. The Fn key is processed inside the keyboard itself and never reaches the operating system. Keys and combinations the OS or browser reserves — the Windows/Command key on some systems, Ctrl+W, Print Screen on certain platforms — may act before this page can observe them. Many keyboards also ship with the F row defaulting to media functions: until F-Lock (or Fn) is used, the F keys send media codes, which register here as extra keys rather than lighting the F row. Everything else, including function keys, media keys, and numpad keys, registers normally; keys that aren't drawn on the diagram still appear in the readout and the extra-keys list.

Frequently asked questions

Why doesn't my Fn key show up?
The Fn key is handled inside the keyboard's own controller and never reaches the operating system, so no browser or software tester can see it. To test Fn, press an Fn combination (like Fn+F5) and check whether the combined action registers instead.
Why do some keys not respond even though they work elsewhere?
Browsers and operating systems reserve a few shortcuts: the Windows/Command key usually registers on press but then opens the system menu, and combinations like Ctrl+W act before the page can see them. Print Screen on Windows only reports when released, so it lights the moment you let go. And if the F row triggers volume or playback actions instead of lighting F1–F12, the keyboard itself is in media mode — toggle F-Lock (or hold Fn) to send true F-codes. These are platform behaviors, not broken keys.
What is key rollover and ghosting?
Rollover is how many keys your keyboard can register at once. Hold down several letters and watch the rollover counter: budget keyboards often max out at 6 keys or drop certain combinations (ghosting), while NKRO keyboards register everything. This matters mostly for gaming and fast typing.
Does this work with AZERTY, QWERTZ, or other layouts?
Yes. The tester listens to the physical position of each key (the KeyboardEvent code), not the printed legend, so every physical key lights up correctly on any layout. The on-screen labels show US legends, and the readout also shows the actual character your layout produced.
My key double-types. Is it broken?
Rapid repeated registrations from a single press, called chatter, usually mean a worn or dirty switch. Try cleaning under the keycap with compressed air first. On mechanical keyboards a persistent chattering switch typically needs to be replaced; on laptops it usually means a keyboard service.

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