How to test your keyboard
Press every key one by one. Keys pressed at least once change color, and the key you're holding is highlighted. Keys that never change color may have a bad contact.
Checking rollover
Hold several keys at once and check the "Pressed now" count. Ordinary membrane keyboards may not register more than 2–3 keys in some combinations (ghosting); gaming keyboards support 6 or more, or unlimited (NKRO).
When keys miss or double-type
- Remove the keycap and clean out debris.
- On mechanical keyboards it may be a switch contact problem (chattering).
- On laptops, connect an external keyboard to compare.
The Fn key, some media keys and the Han/Eng and Hanja keys may not be passed from the OS to the browser, so they may not show.