How to use this test
- Press every key. Each key lights up as it registers and stays marked once tested, so you can work across the board systematically.
- Watch for keys that stay lit. A key that lights and does not clear when released is stuck — the switch is not returning.
- Hold several keys at once. The rollover counter shows the maximum number of simultaneous keys your keyboard will report.
- Check the chatter count. Any key registering twice from one press is flagged in red on the layout and counted in the readings.
How do I know if a keyboard key is failing?
Keyboards fail in three distinct ways, and telling them apart determines whether you are looking at a thirty-second fix or a replacement. Press every key above and the layout marks each one as it registers — what you are looking for is not just which keys work, but how the failing ones misbehave.
| Fault | Symptom | What you see here | Usual cause |
|---|---|---|---|
| Dead key | Nothing happens when pressed | Key never lights up | Failed switch, broken membrane trace, or debris blocking the plunger |
| Stuck key | Key repeats endlessly or stays held | Key lights and does not clear | Debris under the keycap, or a switch that is not returning |
| Chatter | One press produces two letters | Key highlighted in red | Contact bounce from a worn or dirty switch |
Why is my keyboard typing double letters?
This is chatter, and it is the same physical fault that affects mouse switches. Inside the switch a metal contact closes a circuit when you press. When that contact is worn or contaminated it bounces — making and breaking contact several times over a few milliseconds before settling — and your computer reads the bounce as multiple keystrokes.
Every keyboard applies a debounce filter in firmware to suppress that. Chatter is what happens when the bouncing outlasts the filter window, which is why it develops gradually and is intermittent at first. We flag any key that reports twice within 22 milliseconds, which is below what a human finger can produce, so a healthy key scores zero no matter how fast you type.
Fixing a chattering key
- Compressed air under the keycap. On a mechanical board, pull the cap first with a puller. Debris is behind a surprising share of chatter and this costs nothing.
- Isopropyl alcohol into the switch. A drop through the top opening, then press the key fifty times to work it across the contacts. Let it dry before use.
- Swap the switch. On a hot-swap board this takes seconds and needs no soldering. On a soldered board it is a straightforward but slower job.
- Raise debounce in firmware. If your board runs QMK or VIA, increasing the debounce window hides a marginal switch at the cost of a millisecond or two of latency.
- Replace the board. On membrane keyboards chatter usually means the sheet itself is degrading, and that is not economically repairable.
Why is one of my keys not working?
Before assuming a dead switch, rule out the things that are not faults at all:
- The key never reaches the browser. The Windows key, Print Screen, and most media keys are captured by your operating system before any web page can see them. Those showing as untested here is normal and expected.
- It needs a modifier. Function keys on laptops frequently require Fn to send their standard code, and some boards ship with the function row inverted by default.
- A layer or lock is active. Programmable boards can be left on a secondary layer, and a stuck modifier makes ordinary keys produce nothing recognisable.
If an ordinary letter key does not register with none of the above applying, it is a genuine fault. Start with compressed air under the keycap, then isopropyl into the switch, then a switch swap. On membrane boards a dead key usually means a broken conductive trace, which is repairable with conductive paint but rarely worth the effort.
How do I fix a stuck key?
A key that lights up above and does not clear when released is stuck down. Pull the keycap off, blow compressed air into the switch housing, and work the stem up and down a few times by hand. If it still binds, a drop of isopropyl alcohol and fifty presses will usually free it.
On membrane keyboards a stuck key more often means liquid damage. Sugar in particular leaves a residue that glues the membrane layers together, and that needs the board opening and the sheets cleaning individually with distilled water.
What is key rollover, and does NKRO matter?
Keyboard switches are not wired individually. They sit in a grid, sharing row and column conductors, and the controller scans that grid to work out which keys are down. This keeps the wiring simple but creates an ambiguity: for certain combinations of three or more keys, several different sets of presses produce an identical electrical pattern.
Faced with that ambiguity a keyboard has two options. It can guess, which produces ghosting — a key you never touched appearing on screen. Or it can refuse, which produces blocking — one of your real presses being dropped. Modern keyboards all choose blocking, because a missing keystroke is far less damaging than an invented one.
The fix is a diode behind every switch, making each key electrically distinct. Keyboards built that way advertise NKRO, meaning any number of keys can be pressed at once. Boards without diodes typically manage six, which is also the limit of the standard USB keyboard protocol.
Hold several keys down at once above and the rollover reading shows your board's real limit. For typing, three is plenty. For gaming, six or more matters, because movement plus a modifier plus an action key reaches the limit quickly.
Related tests
The same contact-bounce fault affects mouse switches — the double click test measures it there, and if your keyboard is chattering it is worth checking whether your mouse has started to as well. If you are checking a whole setup, the mouse button test covers the other half.
Frequently asked questions
How do I test my keyboard keys?
Press every key on your board and watch the layout above. Each key lights up as it registers and stays marked once tested, so you can work across the keyboard systematically and see at a glance which keys have not responded. Hold several keys at once to probe your rollover limit, and watch for any key that lights up and does not clear when you release it, which indicates a stuck switch.
Why is one of my keyboard keys not working?
Check first whether the key is intercepted before the browser sees it — the Windows key, Print Screen and most media keys are handled by the operating system and never reach a web page, so those showing as untested is normal. Function keys on laptops often need the Fn modifier. If an ordinary letter key does not register at all, that is a genuine fault: a dead switch, a broken trace on the membrane, or debris under the keycap. Blow compressed air under the cap first, since debris is behind a large share of dead keys.
Why is my keyboard typing double letters?
That is key chatter — a single press registering as two or more keystrokes because the switch contact bounces instead of closing cleanly. This test flags it in red on the layout. On a mechanical keyboard, blow compressed air under the keycap first, since debris causes a large share of cases. If your board is hot-swappable, replacing the switch takes seconds and needs no soldering. On boards running QMK or VIA firmware you can raise the debounce time, which masks a marginal switch. On membrane keyboards chatter usually means the sheet is degrading.
How do I fix a stuck key?
A key that lights up here and stays lit is stuck down. Usually this is debris under the keycap or a switch that is not returning. Pull the keycap off with a puller, blow compressed air into the switch housing, and work the stem up and down a few times. If it still binds, a drop of isopropyl alcohol into the switch and fifty presses will often free it. On membrane keyboards, a stuck key more often means liquid damage, which needs the board opening and the membrane cleaning.
What is key rollover and what does NKRO mean?
Rollover is how many keys your keyboard can report simultaneously. Cheap membrane keyboards often manage only two or three before extra presses are dropped, because the key matrix cannot distinguish certain combinations. 6KRO means six simultaneous keys plus modifiers, which is the USB standard. NKRO means unlimited, achieved by putting a diode behind every switch so each key is electrically distinct. For typing, anything above three is fine; for gaming, six or more matters because movement plus modifiers plus an action key adds up quickly.
Why does holding three keys sometimes drop one?
That is ghosting, and it is a limitation of how the key matrix is wired rather than a fault. Keys share rows and columns, so certain three-key combinations become electrically ambiguous to the controller. Faced with that ambiguity a keyboard can either guess, producing a key you never pressed, or refuse, dropping one of your real presses. Modern keyboards all choose to drop, because an invented keystroke is far more damaging than a missing one.
Does this test work for laptop keyboards?
Yes, entirely. The layout shown is a standard full-size ANSI board, so a laptop will have fewer keys than are displayed — that is expected, and the untested count will not reach zero. Everything your laptop does have will register and be checked normally.