Keyboard Ghosting, Dead Keys and Stuck Keys: How to Tell Them Apart

Three very different keyboard faults get reported the same way: "a key is not working". A dead key never registers. A stuck key registers when you are not pressing it. Ghosting means a key you really did press was dropped because you were holding other keys at the same time. They have different causes and different fixes, and a browser test separates them in a couple of minutes.

Open the keyboard test and press keys one at a time. Every key that registers lights up on the on-screen keyboard, so the keys that stay dark are your shortlist.

Dead key: nothing happens

A dead key produces no input at all. On the test page it never lights up, and the key counter does not move. Common causes are debris under the keycap, a worn or contaminated membrane contact, liquid damage, or a broken trace in the keyboard matrix.

Before assuming hardware, rule out two software cases: a keyboard layout that maps that physical key somewhere else, and a remapping utility or game overlay that has captured the key. Switching to the default system layout and closing remapping software takes a minute and occasionally solves the whole problem.

Stuck or repeating key: input you did not ask for

A stuck key sends input on its own — a character that repeats forever, a modifier that behaves as if it is held down, or a cursor that drifts. The usual causes are physical: debris or dried liquid holding the key down, a damaged stabiliser on a large key, or a switch that no longer returns.

There is also a well-known software cause worth checking first. Accessibility features such as Sticky Keys and Filter Keys change how held and repeated keys are interpreted, and they can be switched on accidentally by pressing a key several times in a row. Check your accessibility settings before opening anything.

Ghosting and rollover: the key you pressed was dropped

Ghosting is different from the other two, because the key itself is usually fine. Keyboards read their keys through a grid of rows and columns rather than one wire per key. With certain combinations held down at once, that grid becomes ambiguous — the controller cannot tell which keys are genuinely pressed, so it drops one or reports one you did not press.

The related term is rollover: how many keys the keyboard can report simultaneously. Keyboards advertised with n-key rollover are designed to report every key you hold at once. Many keyboards report a smaller fixed number of simultaneous keys plus modifiers, which is fine for typing and only becomes visible in games or shortcuts that need several keys at once.

To check it, hold three or four keys you actually use together — for example the movement cluster plus a modifier — and watch how many register on the test page. If the fourth key never appears while all four work fine individually, you are seeing a rollover limit, not a broken key. That is a design characteristic of the keyboard, not a fault you can repair.

What a browser keyboard test can and cannot see

The test reads the key events your operating system passes to the page. That is enough to confirm which keys register, what each key reports, and how many keys survive a simultaneous press in that browser.

It cannot see keys that never reach the browser. Function keys, screenshot keys, media keys, browser shortcuts and system shortcuts are frequently intercepted by the operating system or by the browser itself, and some laptop keys are handled entirely in firmware. A key that stays dark for that reason is not necessarily broken — confirm it somewhere outside the browser before you conclude anything. Treat the result as a practical self-check, not a hardware diagnosis.

Test it properly

1. Open the keyboard test and press Reset.
2. Work across the keyboard row by row, pressing each key once, and note which keys never light up.
3. Press and hold a single key to check it repeats normally and stops when you release it.
4. Hold three or four keys at once to check rollover for the combinations you actually use.
5. Re-test any suspect key after a restart, with the default keyboard layout, and with remapping software closed.

Cleaning, safely

If a key feels gritty or sticks physically, start with the least invasive option: power the keyboard down, turn it over and shake the debris out, then use short bursts of compressed air. On a desktop keyboard with removable keycaps, a keycap puller lets you clean underneath without force — check whether your keyboard supports that before pulling anything.

Do not pour liquid into a keyboard, and do not lever keycaps off a laptop keyboard: laptop key mechanisms are small, clipped in place, and easy to break permanently. If the keyboard is under warranty, a reproducible dead or stuck key is a normal warranty claim; warranty terms vary by brand, model and country, so check the terms that apply to your purchase before opening anything.

Quick reference

• Never registers, alone or in combination — dead key. Check layout and remapping software, then hardware.
• Registers without being pressed, or repeats endlessly — stuck key. Check accessibility settings, then debris.
• Works alone, disappears only in combinations — ghosting or a rollover limit, not a broken key.
• Never reaches the browser at all — likely intercepted by the system; verify outside the browser.

While you are testing your input devices

Keyboards are rarely the only worn input device on a desk. If your mouse has started registering two clicks from one press, that is a separate and equally common fault — run the mouse test and see why a mouse double-clicks on one press.

Start with the keyboard test: it costs a minute, and it tells you which of the three problems you actually have before you buy a replacement.