Keyboard Tester

The Keyboard Tester checks every key on your keyboard from inside your browser and tells you exactly which ones are failing. Press a key and it lights up on the visual layout; any key that stays grey never reached the computer, which is what a dead key is. Beyond the basic light-up test, this tester also catches the two faults that plain testers miss — switch chatter, where one press registers twice, and stuck keys, which never release — and measures your keyboard's rollover, the number of keys it can report at once. Nothing you press leaves your device.

How a Keyboard Tester Works

Every time you press a key, the browser fires a keydown event, and when you let go it fires a keyup. Those two events are the entire conversation between your keyboard and any program on your computer. A keyboard tester simply listens for them and draws what it hears. That is why the test is meaningful: if a key produces no keydown here, it is producing no keydown anywhere, so the problem is the keyboard rather than the game or document you were fighting with.

This tester reads the code property of each event rather than the key property. The difference matters. key reports the character your layout produces, so the same physical switch is "q" on QWERTY and "a" on AZERTY. code reports the physical switch itself, always KeyQ, regardless of layout or language. Since a hardware fault belongs to the switch and not to the character, following code is the only way a keyboard test can be honest for every user in the world.

The Three Faults This Tester Finds

How to Test Your Keyboard

1. Pick your board: Choose ANSI (US) or ISO (UK and Europe), then full-size, TKL or 60%. Coverage is scored only against the keys your board actually has, so a laptop is never marked down for a numpad it does not own.
2. Click the keyboard area: The status badge turns green and the tester starts capturing. While it is listening, keys like Tab and Space are intercepted so they test instead of scrolling the page. Press Esc twice to release the keyboard again.
3. Press every key once: Work methodically across the board. Each key turns green as it responds and darkens the more times you hit it, so a key you have hammered while hunting an intermittent fault is easy to spot.
4. Hold several keys together: This measures rollover. Mash six or more keys at once and watch the highest number your keyboard is willing to report.
5. Read your report: Click See My Keyboard Report for a health score, a list of every key that never responded, and details of any chattering or stuck switches.

Why Some Keys Cannot Be Tested

A few keys never reach the browser, and no web-based keyboard tester can see them. This is a security boundary rather than a fault in your keyboard:

• Fn is handled entirely inside the keyboard's own controller. It changes what the other keys send and never sends anything itself, so the browser has no idea it exists.
• F12 and other browser-reserved shortcuts are claimed by the browser before any page sees them.
• Media keys, power and sleep are usually consumed by the operating system.
• Ctrl+Alt+Del is intercepted by the operating system at a level no application can reach.

If one of these keys is your problem, test it outside the browser: Fn is best checked by seeing whether the function it triggers actually happens, such as the brightness or volume changing.

Keyboard Rollover Explained

Rollover is how many keys your keyboard can report pressed at the same time. It is decided by the wiring of the switch matrix and by the USB protocol, not by the quality of the switches, so it never degrades with age — a keyboard with 2-key rollover left the factory that way.

Note that the number you measure here is the lower of what your keyboard supports and what your browser and operating system pass through. If you know your board is NKRO but the test reports six, the limit is almost certainly the USB boot protocol rather than the keyboard.

How to Fix a Dead or Chattering Key

Most key faults are dirt, not death, and the fix costs nothing:

1. Unplug the keyboard or switch off a wireless one before touching anything.
2. Pull the keycap off. A keycap puller is safest, but two fingers and steady upward pressure work on most boards.
3. Blast the switch with compressed air to move loose debris. This alone fixes a large share of chattering keys.
4. Clean the contacts with isopropyl alcohol if air is not enough. A few drops into the switch, then press the stem twenty or thirty times to work it through, and leave it to dry completely.
5. Swap the switch if the fault survives cleaning. On a hot-swap mechanical board, pull the old switch out and push a new one in — no tools, no soldering. On a soldered board this needs a soldering iron and some patience.
6. Re-test here after every step, so you know whether it worked before you reassemble everything.

For a membrane or laptop keyboard, a dead key that survives cleaning usually means a damaged membrane layer or a broken trace, and neither is economically repairable — an external keyboard is the usual answer.

Testing a Keyboard Before You Buy It

If you are buying a used or refurbished keyboard, run this test before the return window closes. Press all 104 keys, check that coverage reaches 100%, then hold six or more keys together to confirm the rollover matches what the seller claimed. A used mechanical keyboard with a single chattering switch is still a good buy if it is hot-swappable, and a bad one if it is soldered. The report names the exact switch, which is what you need for the replacement.

Frequently Asked Questions

How do I know if a key is dead?

Press it while the tester is listening. Every working key lights up green the moment it sends a key event to the browser. If you press a key firmly and it stays grey, the browser never received anything from that switch, which is exactly what a dead key means. The report lists every key that never responded, grouped by area of the keyboard, so you can go back and press only those.

What is keyboard chatter?

Chatter is when one physical press produces two or more key presses. Inside a mechanical switch the metal contacts bounce for a few milliseconds when they close, and the keyboard firmware is supposed to hide that with a debounce delay. As a switch wears out or collects dust, the bouncing outlasts the debounce window and the extra presses leak through. The tester flags a key as chattering when a second press arrives less than 40 milliseconds after the first, which is far faster than any human can deliberately double-tap.

What is a stuck key?

A stuck key is one that reports as held down when you are not pressing it, usually because the keycap or switch stem is physically jammed. Every normal press sends a keydown followed by a keyup. A stuck key sends the keydown and never sends the keyup, so the computer behaves as though you are leaning on that key forever. The tester flags any key that stays down for more than six seconds or is still down when you ask for your report.

What is keyboard rollover and NKRO?

Rollover is how many keys your keyboard can report at the same time. Budget membrane keyboards often manage only two or three because their switch matrix cannot tell certain combinations apart, standard USB keyboards manage six, and boards advertised as NKRO or n-key rollover can report every key at once. Hold several keys down together during the test and the tester records the highest number your keyboard reported. A low number is a design limit, not a fault, and it does not change as a keyboard ages.

Why does my keyboard tester show the wrong letters?

It does not — the tester deliberately shows physical key positions rather than the characters your layout produces. It reads the browser code property, which names the physical switch, instead of the key property, which names the character. That means the key next to the left Shift lights up in the same place whether you use QWERTY, AZERTY or Dvorak. A hardware test has to follow the switch, because that is the part that can fail.

Can I fix a dead or chattering key myself?

Often, yes. Most dead and chattering keys are caused by dust, crumbs or spilled liquid under the keycap rather than by a broken switch. Unplug the keyboard, pull the keycap off, and clean the switch with compressed air followed by isopropyl alcohol. If a mechanical keyboard has hot-swap sockets you can simply pull the failing switch out and push a new one in. If the fault survives cleaning and the board is soldered, the switch itself has worn out and needs desoldering, or the keyboard needs replacing.

Additional Resources

• Contact Bounce (Switch Chatter) - Wikipedia
• Keyboard Event Code Values - MDN