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Press keys and watch them light up: dark while held, tinted once tested. A key that never reacts isn't sending anything to the computer — which separates "broken switch" from "software problem" faster than any other diagnosis. The readout also shows the exact key and code your keyboard sends, which is what developers need when debugging shortcuts.
Browser and system shortcuts are suppressed while you're on the page, so Tab, Space and friends can be tested safely.
Frequently asked questions
A key works here but not in my game or app — why?
Then the hardware is fine: the app is the problem. Check its key bindings, conflicting shortcuts, or whether it distinguishes left/right modifiers — this tester shows exactly which variant (e.g. ShiftLeft vs ShiftRight) your key sends.
A key doesn't light up at all — is it dead?
Test it in another app to confirm. If it's dead everywhere: on a mechanical keyboard, suspect the switch (often replaceable); on a laptop, debris under the key is the common culprit before the keyboard itself.
Why does my layout look different from the one shown?
The display uses a standard US layout, but every key you press registers regardless of your physical layout — watch the last-key readout, which reports exactly what your keyboard sent.