Mac Keyboard Tester

By default, macOS uses the top row for brightness, Mission Control and volume, and handles those keys before the browser sees them. Hold fn while pressing the top row, or turn on “Use F1, F2, etc. keys as standard function keys” in System Settings › Keyboard.

macOS doesn’t report key releases while Command is held. The tester clears held keys when you let go of Command, so nothing stays stuck.

Not in a browser. macOS handles fn/Globe and Touch ID itself and never passes them to web pages, which is why they’re greyed out. Test fn by holding it with a top-row key: F1 to F12 should then light up.

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.

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.

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.