75% Keyboard Tester

Turn it both ways and press it. Most knobs send volume up, volume down and mute. Some browsers receive these and list them under “Also detected”. Others hand them to the operating system first, so check that your system volume changes. A knob remapped in VIA or the maker’s app sends whatever you assigned it, and you’ll see that key here.

Nothing. The keyboard is set to send media keys by default. Hold Fn while pressing F1 to F12, or change the default in the keyboard’s software or with its Win/Mac switch.

Fn is handled inside the keyboard. It switches the keyboard to another layer and is never sent to the computer, so no browser-based tester can see it. Test it by holding Fn and pressing a key on that layer, for example Fn + 1 for F1. The key it sends should light up here.

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.