Keyboard test — find dead keys and check N-key rollover
When a key stops registering, or types on its own. Press through the board and see exactly which key is at fault.
Test a keyboard in the browser with no sign-up. Check that every key registers, find keys that do not respond or fire on their own, and read how many keys the board accepts at once.
Click this area once, then press keys. Any key you have pressed keeps its colour. The same key arriving twice within 60ms counts as chatter. Auto-repeat from holding a key is not counted.
Last input —
Working out why a key stopped responding
If one key alone fails, the switch or the keycap is the likely cause. Press that key in the tester above and check whether it changes colour — that single observation splits "the board never received it" from "the board received it and something downstream ate it." If several keys fail together, suspect the cable, the USB port, or receiver interference on a wireless board before you touch a switch.
Why simultaneous input (NKRO) matters
It rarely shows up in document work, but games and shortcut combinations regularly need three or more keys at once. Cheap membrane keyboards stop registering at two or three. Watch the "most at once" figure while you press several keys together and the ceiling appears immediately.
Keys that fire on their own (stuck keys)
A character repeating with nothing pressed means a switch is held down and not returning. Pulling the keycap and clearing debris fixes this more often than people expect; if it persists, the switch needs replacing. On a hot-swap board that is a part swap rather than a repair.
Keys the browser takes first
F11, Ctrl+W, Alt+Tab and similar combinations are claimed by the browser or the operating system and never reach this page. That is a limit of testing in a browser, not a fault in your keyboard.
Rule out software before you pull a switch
People go straight for the switch, and software turns out to be the cause surprisingly often. On Windows, Filter Keys ignores brief presses when it is on (Settings → Accessibility → Keyboard). The key may have been remapped or disabled in the manufacturer's software, and gaming keyboards have a key lock mode that a stray combination can switch on. Plugging the board into a second computer settles it quickly.
If it registers, but only when you press hard
The switch is not dead — the contact has degraded. Debris is the usual cause, so cleaning revives a high proportion of these. Turn the board over and tap it gently; with compressed air, blow from a distance and at an angle. Pull the keycap and press the stem directly: if that registers, the keycap or the stabiliser was binding, not the switch.
When a whole row or column dies
That is the board's matrix wiring or its controller, not individual switches. Keyboards do not wire every key separately; they read a grid of rows and columns, so one broken line kills everything on it. Look at which keys stay uncoloured in the tester above — if they line up along a row or a column, the fault is past normal home repair. Rule out the cable and USB port first on a wired board, or receiver interference on a wireless one.
How to test properly
- Switch to a plain Latin input mode. An active IME changes how key events arrive during composition
- Walk every key. Finding a broken key you never use is worse after the exchange window closes
- Test the combinations you actually hold together — WASD, the arrow cluster, Ctrl+Shift pairs
Read next
Other checks, including typing speed and mouse input, are on the tools page.
Frequently asked
A key does not show up here but works elsewhere.
It is being claimed before the page sees it. Combinations like F11, Ctrl+W, Alt+Tab and Cmd+Q are taken by the browser or the operating system and never reach a web page. That is a structural limit of browser testing, not a fault in the keyboard.
How many simultaneous keys is enough?
Two or three covers document work. If you game or lean on shortcuts, six is the practical line, and full N-key rollover is rarely necessary. Cheap membrane boards cut out at two or three, and some have blocking that only appears on particular combinations — so test the combinations you actually hold.
Is replacing just the keycap worth trying?
Yes, it is worth checking. A cracked keycap stem or a binding stabiliser can stop the switch travelling fully. Pull the keycap and press the stem directly: if that registers, the keycap is the problem and swapping it with another one fixes it.