How to test your keyboard
Every key once
Pick your layout above, then press each key one by one. Keys turn green when they work. Any key that stays grey is dead or not reaching the computer.
Several at once
Hold down as many keys as you can together – for example A S D F J K L. “Max at once” shows your rollover. If a key you hold does not light up, that is ghosting.
Watch for red
A key turns red when a single press is registered twice within 30 ms. That is key chatter – the cause of double letters when you type.
What the results mean
| Reading | Meaning |
|---|---|
| Keys tested | How many keys of the chosen layout have registered at least once. When it reaches the total, every key works. |
| Max at once | The most keys held down at the same time. Cheap office keyboards often stop at 2–6 keys in some combinations; gaming keyboards with N-key rollover (NKRO) register all of them. |
| Chatter | Presses that arrived twice within 30 ms of releasing the key. Your finger can't do that, so on a healthy keyboard this stays at 0. |
| Last press | How long you held the last key. A key that “sticks” shows unusually long holds or stays lit after you let go. |
| event.key / event.code / keyCode | What the browser receives: the character (depends on your layout), the physical key position, and the older numeric key code. Useful for developers and for checking remapped keys. |
| Other keys | Keys that are not on the drawing – media keys, extra macro keys, the ISO key next to Left Shift and so on. They appear as green chips when pressed. |
Common keyboard problems
A key does nothing
If the key stays grey here, check it on another computer. Dead on both usually means a broken switch or a trace on the membrane; on laptops, a liquid spill is a common cause.
Double letters when typing
The key turns red in this test: that is chatter from a dirty or worn switch. On mechanical keyboards, cleaning or replacing the switch fixes it.
Keys missing when pressed together
Low “Max at once” or keys that don't light when combined is ghosting / limited rollover – a design limit of the keyboard, not a fault.
A key is stuck
A key that stays lit after you release it is physically stuck or shorted. Remove the keycap and clean under it, or check for debris.
Wrong characters
If event.code is right but the letter is wrong, your keyboard layout (language) in the operating system doesn't match the keyboard – switch it in Settings.
Fn and media keys
The Fn key is handled inside the keyboard and is never sent to the computer, so no website can test it. Try Fn combinations instead – they show up as their result.
How to fix keys that don't work or type twice
- Try another USB port or computer. This tells you whether the keyboard or the computer is at fault. For wireless keyboards, charge or replace the batteries and move the receiver closer.
- Check Filter Keys and Sticky Keys. On Windows, Settings → Accessibility → Keyboard. Filter Keys can ignore short presses and makes keys seem dead.
- Clean the keyboard. Unplug it, turn it upside down and shake it, then use compressed air between the keys. For a single bad key, remove the keycap and clean around the switch.
- Mechanical keyboards: press the chattering key firmly 50–100 times, or spray a little contact cleaner into the switch. Hot-swappable boards let you replace the switch in seconds.
- Update or reset the keyboard software and firmware, and remove macros or remaps you don't use.
- Laptops: if a key stays dead after cleaning, the keyboard usually has to be replaced – often under warranty.
Testing your mouse too? Try the mouse button test and the double-click test.
Frequently asked questions
Why don't some keys work in the test?
The operating system keeps a few shortcuts for itself: the Windows key combinations, Alt+Tab, Ctrl+Alt+Delete, and on Mac most ⌘ shortcuts. The Fn key never reaches the computer at all. Everything else should light up.
What is N-key rollover (NKRO)?
Rollover is how many keys a keyboard can register at the same time. 6KRO means six keys plus modifiers; NKRO means every key. Hold many keys together and read “Max at once”. Note that some keyboards only enable NKRO in a setting or over a wired connection.
What is keyboard ghosting?
Ghosting is when pressing certain combinations of keys makes one of them not register (or makes a key you didn't press appear). It comes from how the key matrix is wired, and is common on cheap keyboards. Gaming keyboards add “anti-ghosting” for popular key groups like WASD.
Why does PrintScreen only light up briefly?
On Windows the PrintScreen key only sends a key-release event to the browser, so the test marks it as working when you let go.
Can I test a laptop keyboard?
Yes – choose the “Laptop” layout. Keys like Home or Page Up that need Fn on your laptop appear under “Other keys” when pressed.
Does this work on a phone or tablet?
Only with a physical keyboard connected (USB or Bluetooth). On-screen keyboards don't send real key codes.