Full-Size Keyboard Tester

No. The tester reads which physical key you pressed, so numpad keys light up whether Num Lock is on or off. If a numpad key doesn’t register either way, the key or switch is at fault.

Yes. Every key that exists on your board lights up here. Keys arranged differently still register because the tester follows key codes, not positions. Keys this map doesn’t show appear under “Also detected”.

Rule out the setup first. Try another USB port or cable, charge or re-pair a wireless board, check any Windows/Mac mode switch, and try another computer. If a key still doesn’t register on a hot-swap board, swap its switch with one from a key you rarely use. If the fault moves with the switch, replace the switch. If it stays in place, the socket or circuit board is at fault. On soldered boards and laptops, clean under the keycap first. A key that stays dead usually means a repair or a new keyboard.

Chatter is when one press types a letter twice. It usually comes from a worn or dirty switch, or firmware that doesn’t filter contact bounce. The tester flags a key when a second press arrives less than 50 ms after the first. Even fast deliberate tapping leaves about 100 ms between presses, so anything quicker is the switch, not you. Holding a key down (auto-repeat) never counts as chatter, and you can change the threshold to 30 or 80 ms.

Hold several keys at once, such as A, S, D, F plus J, K, L. The “at once” count above the keyboard shows the highest number registered together. Many USB keyboards handle 6 keys plus modifiers (6KRO), while N-key rollover boards register every key. If a key you’re holding doesn’t light up, the keyboard is blocking that combination. If a key you didn’t press lights up, that’s ghosting.

Media and brightness keys are often handled by the operating system before the browser sees them, so some may never light up. When they do reach the browser, they appear under “Also detected”. On Windows, Print Screen only reports its release, and the tester counts that. Browser shortcuts such as Ctrl+W are never blocked, so you can’t lose this tab by accident.