What to look for
A key that never registers is usually debris or a failed switch. A key that registers twice from one press is switch bounce, common as a mechanical keyboard ages and often the first sign a switch needs replacing. A key that sticks on shows here as staying lit.
Worth testing the whole board rather than the keys you noticed — problems cluster, and it takes a minute.
Rollover, and why gaming keyboards advertise it
Membrane keyboards wire keys in a grid, and certain combinations become ambiguous — press three keys in one region and the fourth registers nothing, or a phantom key appears. That is "ghosting", and it is a limitation of the wiring rather than a fault.
N-key rollover keyboards wire each key independently, so any number can be held at once. Hold several here and see how many the board reports; on a cheap membrane board it is often three.
The keys the browser keeps
Some combinations never reach the page: the Windows key, Command+Tab, and F11 in some browsers are handled by the operating system first. Their absence here is not a fault in the keyboard.
Frequently asked questions
A key registers twice from one press. What is wrong?
Switch bounce — the contacts making and breaking rapidly. It is a common ageing failure on mechanical keyboards and usually means replacing the switch.
Why do some keys stop working when I hold several?
Ghosting, from how membrane keyboards are wired. It is a design limit, not a fault. N-key rollover boards do not have it.
Why does the Windows key not show?
The operating system takes it before the browser sees it. The same applies to Command+Tab and some function keys.
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