Keyboard Test — Find Dead or Stuck Keys

How to test your keyboard

1. Click once anywhere on this page

   The page needs keyboard focus before it can receive key events.

2. Press every key on your keyboard

   Each key turns green the first time it is detected and blue while it is held down.

3. Look for keys that stay grey

   A grey key after you have pressed it is a key the browser never received.

4. Hold several keys at once

   This reveals ghosting limits — how many simultaneous presses your keyboard can actually report.

5. Check the event log

   The log shows the exact key, code and keyCode for the last presses, which is useful when a key produces the wrong character.

Dead keys, sticky keys and chattering keys

Keyboards fail in three distinct ways, and the on-screen board above distinguishes them clearly.

A dead key never lights up. The switch has failed, the contact is dirty, or the trace on the membrane underneath has worn through. On a mechanical keyboard a single dead switch is replaceable; on a membrane keyboard the whole sheet is one part, which is why laptop keyboards are usually replaced as an assembly.

A sticky key lights up and stays lit after you release it. The switch is not springing back, almost always because something is under the keycap. On a mechanical board you can pull the cap and clean underneath; on a laptop, compressed air at an angle removes most debris.

A chattering key fires more than once from a single press. Watch the event log — if one press produces two or three down events, the switch contacts are bouncing. This is the keyboard equivalent of the mouse double-click fault, and it means the switch is wearing out.

Understanding ghosting and rollover

Hold down three or four keys at once and count how many stay lit. What you are measuring is rollover: how many simultaneous presses the keyboard can report accurately.

Cheap membrane keyboards wire their keys in a grid to save on components, and that grid cannot always tell which combination of keys is held. The result is either a missing key or a phantom key that was never pressed — the original meaning of "ghosting". Most such keyboards manage two or three simultaneous keys reliably, which is fine for typing and frustrating for games where you might hold forward, strafe, sprint and jump at once.

Keyboards advertised with N-key rollover place a diode behind every switch so any number of keys can be reported independently. Six-key rollover is the practical limit over standard USB HID; full N-key rollover requires the keyboard to present itself differently to the system. If you play games competitively, testing this before you buy is worth the two minutes.

Why some keys never appear

Key	Does it reach the browser?	Why
Fn	No	Handled inside the keyboard's own controller; the computer never sees it as a key
Print Screen	Sometimes	Intercepted by the operating system's screenshot handler
Media and volume keys	Usually not	Consumed by the OS audio layer before reaching applications
Caps Lock, Num Lock	Yes	Reported normally, though the light state is controlled by the OS
Windows / Command	Yes, briefly	Registers, but may also open the system menu
Alt+Tab, Ctrl+W and similar	No	Reserved by the OS or browser for window management

Cleaning a keyboard properly

Most "broken" keys are dirty keys. Turn the keyboard upside down and shake gently first — the amount that falls out is usually surprising. Then use compressed air held at a shallow angle rather than straight down, so debris is pushed out from under the cap rather than deeper into the switch.

For a mechanical keyboard, a keycap puller costs very little and lets you clean the switch directly with isopropyl alcohol on a cotton bud. For a laptop, resist the urge to pry keycaps off; the retaining clips are fragile and cost more to replace than the cleaning was worth. If liquid has been spilled, power off immediately, turn the machine upside down, and do not switch it back on for at least 48 hours.