How do I test for a dead key?

Press it and watch the matching key on screen. If it never lights up, it's not reaching the browser. Usually that means a dead key. Fn and a top-row key in media mode are the exceptions, since they stay dark even on a healthy board.

Why does a key register twice when I press it once?

That's chatter, usually from worn or dirty switch contacts that bounce and fire a second signal. You'll notice it as a doubled letter when you type normally. Cleaning or swapping the switch fixes it.

What is key ghosting and how do I test it?

Ghosting is when a keyboard can't report several keys held at once. Hold three or four together, like W, A, and Shift. Then add one more. If the new key never lights, or a held one goes dark, that combination ghosts. Press the dark key on its own to make sure it works. Snap Tap and SOCD break this for A and D. With either on, pressing D releases A by design, so A going dark is the feature, not a fault. Run the keyboard ghosting test

How many keys can I hold at once?

It depends on the board. Many keyboards over USB report up to six keys plus modifiers (6-key rollover), the default HID limit. Boards with N-key rollover register every key. Hold a handful and count how many stay green. Run the keyboard ghosting test

Why doesn't a top-row F key light up?

Many laptops and Mac keyboards set the top row to media actions like volume and brightness by default. Hold Fn or turn on Fn Lock, and you get F1 to F12. Fn won't light either. The keyboard usually acts on it internally and sends the browser nothing.

Why does the wrong key light up?

The tester matches by physical key position (event.code), so a non-US layout can map differently. The position is correct even if the printed legend differs.

Is this keyboard tester free?

Yes. It runs in your browser with no software to install. There's no account, no upload, and it works with any keyboard, any brand.

Keyboard Tester

Test every key on your keyboard online. Press each key to see it light up live and catch dead keys, stuck keys, ghosting, and rollover limits, no install.

Vadim Cheban October 14, 2026

Keys tested

Last key

press any key

Click anywhere on the page, then press each key in turn. Dark after a press means the key isn't reaching the browser. Green after you let go means it's stuck. Fn and any key your board lacks stay dark, and that's normal.

Press keys on your keyboard and watch them light up on the layout above. A dead key, a stuck switch, or a chord that ghosts shows itself the moment you hit it.

How to use

Focus the page. Click anywhere on the page so it receives keyboard input, then start pressing keys.
Press every key. Work across the whole keyboard. Each key turns green while held and stays marked as tested after you release it.
Check for problems. A key that stays dark when you press it isn't getting through. Still green after you let go? It's stuck. Hold a few keys and add one more. When the new key won't light or a held key drops out, your board can't report that combination.

Why test this

Keyboard faults are usually intermittent and specific, which makes them maddening to pin down in normal typing. One key misses a press in twenty. A combination silently drops an input mid-game. Mapping every key to a live on-screen layout turns that vague suspicion into something you can see. Run it before buying a used keyboard, after a cleaning or a spill, when a game keeps ignoring a movement key, or to confirm a new board registers everything before the return window closes. The test also exposes ghosting and rollover limits, which matter most for gaming. Cheaper membrane boards often can't report several simultaneous presses, so a crouch-jump-strafe combo loses an input at the worst moment. Once you see which keys and combinations fail, you know whether to clean a switch, claim the warranty, or rebind around a hardware limit.

What the results mean

Press a key and it lights green at once, then keeps a mark after you let go. Every key your board has should light up. Keys it doesn't have stay dark, like the number pad on a tenkeyless. A key that never lights, even pressed on its own, isn't reaching the browser, so it's likely dead. One that stays green after you release it is stuck on. To check rollover and ghosting, hold several keys at once and watch the diagram. If the key you add stays dark while the others stay lit, or a held key drops off, that's ghosting, a limit of the keyboard rather than a broken switch. A and D are the exception on a board with Snap Tap or SOCD turned on, which drops one of the pair by design. Matching is by physical position, so on a non-US layout the highlighted key may not match the printed legend even though the position is right. Fn won't show up at all, because the keyboard keeps it. A top-row key in media mode sends volume or brightness, not its F key.

Example keyboard tester result: every key marked as tested except the E key, which stays dark.

FAQ

How do I test for a dead key?: Press it and watch the matching key on screen. If it never lights up, it's not reaching the browser. Usually that means a dead key. Fn and a top-row key in media mode are the exceptions, since they stay dark even on a healthy board.
Why does a key register twice when I press it once?: That's chatter, usually from worn or dirty switch contacts that bounce and fire a second signal. You'll notice it as a doubled letter when you type normally. Cleaning or swapping the switch fixes it.
What is key ghosting and how do I test it?: Ghosting is when a keyboard can't report several keys held at once. Hold three or four together, like W, A, and Shift. Then add one more. If the new key never lights, or a held one goes dark, that combination ghosts. Press the dark key on its own to make sure it works. Snap Tap and SOCD break this for A and D. With either on, pressing D releases A by design, so A going dark is the feature, not a fault. Run the keyboard ghosting test
How many keys can I hold at once?: It depends on the board. Many keyboards over USB report up to six keys plus modifiers (6-key rollover), the default HID limit. Boards with N-key rollover register every key. Hold a handful and count how many stay green. Run the keyboard ghosting test
Why doesn't a top-row F key light up?: Many laptops and Mac keyboards set the top row to media actions like volume and brightness by default. Hold Fn or turn on Fn Lock, and you get F1 to F12. Fn won't light either. The keyboard usually acts on it internally and sends the browser nothing.
Why does the wrong key light up?: The tester matches by physical key position (event.code), so a non-US layout can map differently. The position is correct even if the printed legend differs.
Is this keyboard tester free?: Yes. It runs in your browser with no software to install. There's no account, no upload, and it works with any keyboard, any brand.

How we measure

Every press and release on this page arrives as a browser key event, and the test finds its tile by the event's code. The code names the physical key, not the character it types, so your layout and Shift don't change it. Codes are named after the US key in that spot, which is why the A key on a French AZERTY board lights Q. The Last key box shows both: what the key typed and its code. On a Mac, Cmd lights the Win key and Option lights Alt. Keys you type into a text box on this page, like the search, don't count.

The board is a full-size US layout with 104 keys: the main block and F row, the navigation keys and arrows, and the number pad. A UK board has one more key, between left Shift and Z. Press it and it joins the board, which then shows 105. The # key beside Enter on a UK board lights the US backslash key, because the browser reports both under one code.

A key turns green while the browser has it down and stays tinted after you let go. Hold a key and it repeats, but the browser marks every repeat and the test skips them. Keys tested counts every different code the page got, including keys with no tile, like volume keys. That count can run higher than the tiles you lit.

Some releases never reach the page, so the test fills them in. Every key event, mouse move and click carries flags for Shift, Ctrl, Alt and Win or Cmd. When a flag is off, that key's tile clears, even if its release got lost. On a Mac, letting go of Cmd also clears the keys you pressed while holding it, because macOS sends no release for them. On Windows, the page gets only the release of Print Screen, so that key counts when you let go. If the page loses focus or you switch tabs, every held key clears, since its release goes to another window.

What a browser cannot see

The page sees only the keys your system passes to the browser. Fn usually stays inside the keyboard and sends nothing, so it has no tile. Your system also keeps some chords for itself, like Ctrl+Alt+Del on Windows and Alt+Tab or Cmd+Tab for switching apps. Check those keys one at a time.

A dark tile only means the page never got that key. A dead switch looks the same as a key the keyboard couldn't report. On the basic USB report, a keyboard sends at most 6 keys plus the modifiers at once. Past that, the USB spec has it send an error code in place of the keys. Linux ignores that report and keeps the keys it already had, so on Linux the newest key stays dark. Let go and press that key alone. If it lights now, the switch works and the combination hit the limit.

The keyboard's own firmware acts before the page sees anything. With Snap Tap or SOCD turned on, pressing D sends a release for A by design, so A goes dark while you still hold it. Key events carry no device name, so with two keyboards plugged in, a key on either lights the same tile. Unplug the one you aren't testing.

Don't count on this test to catch chatter. It keeps no press count per key and no switch timing, so a key that fires twice just flickers, and a flicker looks like one press. To catch a doubled letter, type a few lines in a text editor and read them back.

On a Mac, one case still slips through. A key pressed before Cmd and let go while you hold Cmd can stay green. Press it once more and it clears.

Sources

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