Keyboard tester
Press every key and see which one does not answer. Includes a simultaneous-key test and a ghost repeat detector.
There is no Fn key here: it never reaches the browser or the operating system. The keyboard resolves it internally, and all the computer ever sees is the resulting key — which is why you can test F1 to F12 but never Fn itself.
Some combinations never reach the browser because the operating system takes them first, such as Alt+Tab or the Windows key.
Hold down many keys at the same time. If the counter sticks at 6, your keyboard has the usual USB limit; if it keeps climbing, it has NKRO.
Generated right here, in your browser. What you type never leaves your device.
This tester listens to the keyboard events your browser receives and draws what arrives. Every key you press stays marked, so you can work through the whole board watching your fingers and check the result at the end, instead of looking up after each key.
Nothing you type leaves your machine. The page does not send keystrokes to any server: it only reacts to them and paints them. That matters, because a keyboard tester by definition sees everything you type while it is open.
There are two measurements here beyond "does it answer". The simultaneous-key counter tells you how many keys your keyboard can register at once before it starts dropping them, and the repeat counter catches a key that registers twice without being released — the classic sign of a dirty contact.
How to use it
- 1
Arm the listener
Click the panel at the top so the page starts capturing the keyboard. It does not do this on load: if it did, it would swallow browser shortcuts for anyone passing through on the way to the article below.
- 2
Sweep the whole board
Work through key by key, row by row, without rushing. Keys that answer stay coloured. When you are done, any key still dark is one that never reached the browser.
- 3
Match the board to yours
Pick the size — 60%, 65%, TKL or full — your system, and the layout. This only changes what is drawn: internally the test identifies each key by physical position, so it works even if you pick the wrong size.
- 4
Add the numeric pad if you have one
Hidden by default, because laptops and compact boards do not have one. Turn it on with its button and it appears alongside. Remember to switch Num Lock on before testing it.
- 5
Test simultaneous keys
Hold down many keys at once without releasing any, and watch the "most at once" counter. If it sticks at 6, your keyboard has the usual limit; if it keeps climbing, it has NKRO.
- 6
Watch the ghost repeats
If the repeat counter climbs while you type normally, a key is registering two presses for every one of yours. That is a hardware fault, not a software setting.
Things worth keeping in mind
Membrane
This is what nearly every cheap keyboard and almost every laptop uses. Under the caps sit three plastic sheets: two carrying conductive traces and one in between with holes punched through. Pressing a key pushes a rubber dome down, forcing the top sheet through the hole to close the contact.
Almost none of them have diodes, because a diode costs money and there are more than a hundred keys. That is why these block combinations the most: if this tester gives you a peak of 2 or 3 simultaneous keys, you almost certainly have one. Fine for typing; you notice it while gaming.
- Typical simultaneous peak: 2 to 6 keys
- The rubber dome softens over the years and the key goes mushy or intermittent
- This is the type where ghost repeats show up most as it ages
Mechanical
Every key gets its own independent switch, with its own spring and metal contacts. They can be replaced one at a time, and that is the real advantage: when a key fails you swap that switch instead of binning the keyboard.
Being mechanical does not guarantee NKRO. They are separate things: NKRO depends on there being a diode per switch and on how the keyboard presents itself to the system, not on the kind of spring. Plenty of cheap mechanical boards block combinations exactly like a membrane one.
- Simultaneous peak: 6 under the standard USB protocol, unlimited with true NKRO
- Switches are graded by feel: linear, tactile and clicky
- Commonly rated for 50 to 100 million presses per key
Optical and Hall effect
Instead of two pieces of metal touching, these detect a press by breaking a beam of light or measuring a magnetic field. With no physical contact closing, there is no bounce — and therefore no ghost repeats from wear, which is the most common failure of the other two types.
Hall effect switches also measure how far down the key is, not merely whether it is pressed. That allows the actuation point to be adjusted, and it is what gets marketed as "rapid trigger" on competitive gaming keyboards.
- Effectively immune to the self-repeating key problem
- Nearly always ship with NKRO, since the cost is already elsewhere
- Hall effect boards let you change the actuation point in software
Scissor and laptop
A membrane with a scissor mechanism on top that stabilises the cap and shortens the travel. It is what stops a flat laptop key from tilting when you press one corner of it.
It inherits every membrane limitation and adds one of its own: these are the most sensitive to dirt, because the short travel leaves very little margin before a crumb prevents contact. When a laptop key fails, always start by cleaning.
- 1 to 2 mm of travel, against about 4 mm on a mechanical board
- Usually integrated: replacing one key can mean replacing the whole keyboard
- Debris under the cap is the number one cause of failure
From the typewriter to the switch
Christopher Latham Sholes patented the QWERTY layout in 1878 for the machine Remington would go on to sell. The popular explanation — that he separated common letters to slow typists down — is wrong in its most repeated form. What he wanted was that typebars commonly used in sequence would not swing up from neighbouring positions, because they caught on each other coming back down. It was not about slowing anyone; it was about preventing mechanical jams.
What is true is that the arrangement outlived the machine that justified it. In 1936 August Dvorak patented an alternative placing the most frequent English letters on the home row. Later studies never found the dramatic improvement it promised, and by then millions of typists had been trained on QWERTY. Habit won.
Going electronic introduced a problem the typewriter simply did not have: bounce. A mechanical lever cannot print two letters per strike. Electrical contacts can, and debouncing had to be invented in software.
The IBM Model M of 1985 fixed what we still picture as a keyboard: 101 keys, function row across the top, numeric pad on the right. It weighed over two kilos and its buckling-spring mechanism made a sound people still chase. Units from the eighties are still working and still being sold, which cannot be said of many peripherals from that era.
- 1878
- QWERTY patented
- 1985
- IBM Model M
- ~5 ms
- Typical debounce window
- 6
- Keys in basic USB protocol
What happens between the key and the screen
There is no wire per key under those caps. There is a grid: some traces running in rows, others in columns, and a switch at every crossing. A 104-key keyboard needs about twenty connections that way instead of one hundred and four, and that economy is behind nearly everything strange a keyboard does.
The controller inside sweeps that grid tens or hundreds of times a second: energise a row, see which columns answer, move to the next. That scan is what turns "there is contact at crossing 3-7" into "the J key was pressed".
The trouble starts when you press three keys forming three corners of a rectangle in the grid. Current finds an alternative path and the keyboard also "sees" the fourth corner — a key nobody touched. That is ghosting. The cheap fix is blocking: if the combination is ambiguous, ignore it. That is why on many budget keyboards certain three-key combinations simply do nothing.
The expensive fix is a diode at every switch, stopping current from flowing back the wrong way. That is NKRO — n-key rollover — and it is what lets you press ten keys at once and have all ten register.
Then there is the USB limit, which is a different thing entirely and constantly confused with the above. The basic USB keyboard protocol has room for six keys plus modifiers. Even with diodes throughout, a keyboard speaking that standard protocol will only ever deliver six. Genuine NKRO keyboards use a different mode to escape that ceiling.
Finally, bounce. A metal contact does not close cleanly: it chatters for a few milliseconds, opening and closing several times. The firmware ignores changes arriving too close together, typically within about 5 milliseconds. When that contact wears or gets dirty, the bounces outlast the window and slip through as real presses — that is the key that repeats itself.
Checking for ghosting without any tool
You do not need this tester to find out whether your keyboard blocks combinations. You can provoke it by hand in any text editor.
- 1
Anything you can type into. A browser works too, but a simple editor avoids a shortcut stealing the combination.
- 2
Without releasing any of them. All three letters should appear. If only two do, your keyboard is blocking that combination.
- 3
Try A, S and D, then Z, X and C. Blocking is not uniform: it depends on how the grid is wired, and it usually shows up in some areas and not others.
- 4
W, A and Shift, or W, D and Space. Those are the ones that actually matter if you play, and the ones manufacturers point at to justify the price of the NKRO model.
If something is not working
Symptom:A key never lights up even though I press it
- Likely cause:
- Either the contact is dirty or broken, or the operating system is taking that combination before it reaches the browser.
- What to do:
- Try the key on its own, with no modifiers. If it still does nothing, shut down, unplug the keyboard and turn it upside down, tapping to shake debris out. On a desktop, try another USB port and ideally another computer — that separates the keyboard from the machine.
Symptom:A letter types itself two or three times
- Likely cause:
- The contact bounces for longer than the firmware is set to ignore, usually from wear or dirt.
- What to do:
- Start with cleaning: compressed air around the key with the keyboard face down. If the model allows it, pull the keycap and clean the well. Some manufacturer software lets you raise the debounce time, which masks it. If none of that helps, that switch is worn out.
Symptom:Pressing three keys together, one does not register
- Likely cause:
- That is ghosting blocking: your keyboard cannot tell that particular combination apart and would rather drop it than invent a key.
- What to do:
- There is no fix — it is how the grid is wired. If it affects you while gaming, rebind that action to keys that do coexist; use this tester to find a combination that survives. Only an NKRO keyboard avoids it entirely.
Symptom:I press one letter and a different one appears
- Likely cause:
- The layout the system is set to does not match the one printed on your keycaps.
- What to do:
- Change it in your system language settings. On Windows, Settings → Time & language → Language. Watch out for the shortcut that cycles between layouts — it gets pressed by accident more often than you would think.
Symptom:The whole keyboard stops responding now and then
- Likely cause:
- Usually power or interference rather than the keys: an unpowered USB hub, a failing cable, or a wireless receiver too far away.
- What to do:
- Plug it straight into the computer, no hub. If it is wireless, move the receiver closer with a USB extension and change the batteries. Try a different cable before writing the keyboard off.
Symptom:Function keys do brightness and volume instead of F1 to F12
- Likely cause:
- Not a fault: many laptops ship with the function row inverted by default.
- What to do:
- Hold Fn while pressing to get the opposite behaviour. To flip it permanently, look for "Action Keys Mode" or "Function Key Behavior" in the BIOS, or in the manufacturer software.
Things worth knowing
The top row hides a sales demo
On QWERTY you can spell "typewriter" using only the top row. It is often told as proof Sholes arranged it so salesmen could show off the word. It is probably coincidence, but the word does come out.
The key that outlived its job
Scroll Lock made the arrow keys move the document instead of the cursor, back before the mouse. Almost no program has used it for decades, but it stays because removing it would mean redesigning the whole block.
The bumps on F and J
They are the tactile reference for placing your index fingers without looking. ISO 9995 standardises them, and also specifies another one on the 5 of the numeric pad.
The 6-key limit is not your keyboard
It belongs to the standard USB keyboard protocol, which has room for six keys plus modifiers. A true NKRO keyboard dodges it by presenting itself to the system differently, not by improving the grid.
Typing badly costs more than you think
Backspace ranks among the most pressed keys in any real measurement of typing, ahead of several letters. Correcting takes up a meaningful share of the time we spend at a keyboard.
Frequently asked questions
Does this tester see what I type?
The page reacts to your keystrokes in order to draw them, but it does not store them or send them anywhere. Everything happens in your browser. Even so, the healthy habit is not to type passwords into any page that is listening to the keyboard, including this one.
Why do the Windows key and Alt+Tab never light up?
Because the operating system takes them before handing anything to the browser. No web page can see them, and it is not a fault in your keyboard or in this test.
My keyboard stops at 6 simultaneous keys — is it broken?
No. Six is the ceiling of the standard USB keyboard protocol, so it is normal for most keyboards. Only ones advertising NKRO get past it, and they do so by presenting themselves to the system differently.
Does it work for a laptop?
Yes, exactly the same. If you find a dead key on a laptop, bear in mind the keyboard is usually integrated and replacing it costs more; while you decide, an external USB keyboard works as a stopgap.
What about a wireless or Bluetooth keyboard?
Also fine, as long as the system has already paired it. If you notice occasional dropped keystrokes, that is usually distance, low batteries or interference with 2.4 GHz Wi-Fi rather than the keys themselves.
Why is there no Fn key?
Because it never reaches anywhere you could see it. The keyboard resolves it internally: hold Fn and press F5, and the keyboard decides what to send while the computer only receives the result. Neither the browser nor the operating system ever learns Fn exists, so drawing it would mean drawing a key that could never light up.
Can I test the numeric pad?
Yes, by choosing the 100% size. Smaller formats do not draw one because they do not have one. If its keys do nothing, check Num Lock is on: with it off they send arrows instead.
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