How to test your keyboard for dead or sticky keys

The keyboard test draws an on-screen keyboard and lights each key as you press it.

• Open the keyboard test and click once on the page so it can receive keystrokes.
• Press every key in turn, including function keys, modifiers, the number pad and arrows.
• Watch the on-screen key light up. A key that does not light up did not send a signal to the browser.
• Press and release quickly, then hold a key down, to check it neither sticks nor repeats by itself.

A key that never registers is most often blocked by dirt under the keycap, or has a failed switch or a broken trace on the board. A key that registers twice for one press, called chatter, is typical of an ageing switch. A key that only works when pressed hard points to wear or debris.

Some keys are intercepted by the operating system or the browser before the page sees them, such as the Windows key or certain media keys. If only these are missing, it is a limit of the test, not a broken keyboard.

Ghosting happens when you hold several keys at once and one of them does not register. Cheap keyboards share electrical paths between keys, so some combinations cannot be told apart. Gaming keyboards advertise n-key rollover, which means every key is read independently.

To check, hold a typical gaming combination, for example W, A and Space together, and see whether all three light up on the test. If you play games and a key drops out, that is ghosting and a keyboard with better rollover is the fix.

Unplug the keyboard, or turn the laptop off, before you clean it.

• Turn the keyboard upside down and tap it gently to shake out crumbs.
• Use compressed air at an angle around the affected key.
• Pry off the keycap with a flat tool if you can, and wipe the area with a cotton swab lightly dampened with isopropyl alcohol.
• Let it dry fully before reconnecting. Never pour liquid onto a keyboard.

Before blaming hardware, make sure filter keys or sticky keys are not switched on in the system accessibility settings, that the correct keyboard layout is selected, and that no remapping tool is running. Test in a second browser, or on a second computer, to confirm that the fault follows the keyboard.

If you are checking your desk setup, finish with the mouse test to confirm every button and the scroll wheel respond too.