DeviceCheck Pro

Keyboard test

Press every key. Each one lights yellow while held and stays green once it has registered. Keys that never light up aren’t reaching your computer.

Keyboard
IdleTestingPassFault
Layout:

0 / 104keys registered
0held now
0most held at once (rollover)
–last key

Fn, media and brightness keys are handled by the keyboard or operating system and usually never reach a web page. The Windows/⌘ key and PrintScreen may be captured by the OS.

How to read the results

  • A key never lights up: try it in a text editor too. If it fails there, check for debris under the keycap, try another USB port or re-pair Bluetooth, then test on another computer to rule out drivers.
  • A key lights up late or only when pressed hard: common on membrane and laptop keyboards with worn rubber domes or spilt liquid.
  • A key shows red: it bounced (chatter), sending two presses from one tap.
  • Rollover stops rising: hold W, A, S, D, Shift and Space together. Office keyboards often stop at 2 to 4 keys in some combinations; gaming boards should reach 6 or more.
Event log
  1. Press any key…
Explainer

Why some key combinations fail: ghosting in a key matrix

Keyboards don’t wire each key to the controller. Keys sit at the crossings of row and column wires, and the controller scans them. Press three keys that form three corners of a rectangle, and current can run backwards through them, so the fourth corner looks pressed too. That phantom is a ghost.

To stop ghosts, cheap boards simply block the combination (you see it as a key that won’t register while others are held). Boards with a diode on every switch let current flow one way only, which is how “N-key rollover” is achieved.

Tap keys in the grid. Try Q, W and A together, then switch diodes on.

The controller reads exactly the keys you pressed.

Rollover by connection type

SetupTypical simultaneous keys
Basic office membrane keyboard2 to 3 in some combinations; blocked beyond that
USB “boot protocol” mode6 keys plus modifiers (6KRO)
Gaming or mechanical board in NKRO modeAll keys
Laptop built-in keyboardVaries; often limited in the WASD area

Still not working? Describe it

An AI assistant suggests likely causes and fixes, cheapest first. It sees only what you type. Answers can be wrong; check your device maker’s support pages before opening anything up.

Questions

How do I test my keyboard online?

Click inside the page so it has focus, then press each key. Keys turn yellow while held and green once they have registered. Any key that never lights up is not sending a signal.

Why don’t some keys light up?

Keys like Fn, media keys and some laptop shortcuts are handled by the keyboard firmware or the operating system and never reach the browser. PrintScreen and the Windows key may be intercepted by the OS. That does not mean they are broken.

What is key rollover?

Rollover is how many keys a keyboard can report at the same time. 6KRO means six keys plus modifiers over classic USB; NKRO means every key. Hold keys down one by one and watch the “held now” counter; when it stops rising, you have found your limit.

What is keyboard ghosting?

Ghosting is when the controller reports a key you did not press, because of how the key matrix is wired. Most modern keyboards block the combination instead, so the symptom is a key that refuses to register while others are held.

A key types twice. What does that mean?

Repeated presses from a single tap are usually switch chatter, caused by a worn or dirty switch. This test flags any key that registers twice within 40 ms. Compressed air or a switch cleaner can help; hot-swap boards can have the switch replaced.

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