Test your keyboard for ghosting and key rollover — hold several keys at once and see exactly how many register together.
Simply press any key on your keyboard to test it — if it works it will turn green
0Keys Pressed0Total Keys0%Tested
QWERTY on the US ANSI shape: a wide flat Enter and a full-length left Shift. Standard key positions, with no vendor-specific extras.
Ctrl+W, Ctrl+T, Ctrl+N, Alt+Tab and the Windows or Command key are reserved by the browser and the operating system. No web page receives them, so they cannot be tested here or anywhere else in a browser.
Keys shown greyed out with a dashed outline cannot be tested: your keyboard handles them internally and the browser never receives a key event for them. They are excluded from the totals, so 100% stays reachable.
At a glance
Key counts and layout facts
Detail
Value
What it tests
How many keys report simultaneously
True ghosting
Phantom keys — rare on modern boards
Blocking
Dropped keys — the common failure
Typical USB limit
6 keys plus modifiers
N-key rollover
All keys at once
Modifiers
Reported separately, do not count
Enough for typing
2 to 6 keys
Enough for most gaming
6 keys
Ghosting and rollover in numbers
What the limits actually are on the boards you can buy.
3
Keys to start withGhosting only appears once three or more are held together.
6
The USB HID limitSix ordinary keys plus modifiers in a single standard packet.
2
Keys on a basic boardBudget membrane boards commonly stop at two plus modifiers.
0
Limit with NKROEvery key at once, using a diode behind each switch.
How to test keyboard ghosting
Hold keys down together rather than pressing them in sequence.
1
Hold three keys at once
Pick three keys in the same region of the board and press them together, keeping all three down. All three caps should light green simultaneously. A key that fails to light, or a key you never pressed lighting up, is the fault you are looking for.
2
Add a fourth and a fifth
Keep the first three held and add more, one at a time. Count how many stay lit before the next one stops registering. That number is your rollover limit.
3
Test the combinations you actually use
For games, hold W, A, Shift and Space together. For shortcuts, hold Ctrl, Shift and a letter. A board that handles six random keys can still fail on one specific combination, because the limit depends on matrix wiring rather than on count alone.
Ghosting, blocking and rollover
Three different faults that get called by one name.
True ghosting
The keyboard reports a key you never pressed. The matrix cannot resolve which combination of rows and columns closed, so it guesses. Modern boards use diodes to prevent this, making it rare.
Blocking, the common case
The keyboard silently declines to report the third or fourth key. Nothing wrong appears — a key simply does not arrive. Most complaints about ghosting are actually blocking.
Rollover as a design limit
2KRO, 6KRO and NKRO describe how many keys the board reports at once. Six is the standard USB limit and is normal, not a fault.
Modifiers do not count
Shift, Ctrl, Alt and the Windows or Command keys travel in a separate byte of the USB packet. Six-key rollover means six ordinary keys plus any modifiers.
The browser is not the limit
Key events arrive individually and the page tracks them all. What you see here is your keyboard's limit, not a limit of the test.
Everything about this layout
The shape, the trade-offs and what to watch for when testing it.
01
Ghosting versus blocking versus rollover
Three related things get called ghosting, and separating them helps. True ghosting is a phantom key — the keyboard reports a key you never pressed, because the matrix cannot tell which of several combinations you meant. It is rare on modern boards, which use diodes to prevent it.
Blocking is far more common: rather than inventing a key, the board simply refuses to report the third or fourth simultaneous press. Nothing wrong appears; a key you are holding just does not arrive.
Rollover is the term for how many keys a board can report at once. Two-key rollover means two, six-key rollover means six, and n-key rollover means as many as you can physically hold. What most people call ghosting is really a rollover limit.
02
How to run the test
Hold down three keys that sit near each other — Q, W and E is a good start — and check that all three stay lit. Then add a fourth, then a fifth, adding keys around the same area rather than spread across the board.
Then try the combinations you actually use. For gaming that usually means W, Shift and Space together, or A, W and a number key. For typing it means a modifier plus two letters. The point is to test the combinations that matter to you, not to find the theoretical maximum.
Note which combinations fail. The pattern is diagnostic: keys that share a row or a column in the keyboard matrix conflict with each other, so a board that drops Q, W and E together will usually be fine with Q, T and P.
03
Why USB rollover has a limit
Standard USB keyboards use a protocol that reports six keys plus modifiers in a single packet. That is where six-key rollover comes from — it is not a limitation of the switches but of the reporting format.
Boards advertising n-key rollover work around it, either by sending several packets at once or by using a different USB descriptor. Both are well supported, and neither needs a driver on any current operating system.
Modifiers are reported separately from ordinary keys, which is why Ctrl, Shift and Alt do not count against the six. You can usually hold all the modifiers plus six other keys on any board.
04
What rollover you actually need
For typing, two-key rollover is enough and six is generous. Fast typists overlap keystrokes, but rarely more than two or three at a time, and modifiers do not count against the limit.
For most gaming, six-key rollover is genuinely sufficient. The combinations that break it involve holding four or more ordinary keys at once, which happens in rhythm games, some fighting games, and flight or racing sims with many bound axes.
If you have found a specific combination that fails and you need it, that is a real reason to want n-key rollover. If you have not, it is a specification rather than a problem — and this test is how you find out which.
Rollover levels compared
Three levels, and what each one costs.
Simultaneous key limits by rollover type
Rollover level
Keys at once
Found on
In games
How it works
2KRO
2 plus modifiers
Budget membrane boards
Fails on most movement combinations
No diodes in the matrix
6KRO
6 plus modifiers
Most keyboards
Enough for nearly everything
The USB HID standard packet
NKRO
Every key
Enthusiast and gaming boards
No practical limit
A diode behind each switch
6KRO is the standard USB protocol limit rather than a cost saving. NKRO boards work around it by sending several packets or using a different USB descriptor.
When keys drop out together
Four results and what each one means.
1The third key never registers
On the test:Two keys light, the third does nothing while both are held.
Try three keys in a different part of the board. A limit that moves with position is matrix blocking.
Accept 2KRO as normal on budget membrane boards — it is a design limit, not a fault.
Look for an NKRO toggle in the firmware, often Fn plus N on boards that support it.
Expect to replace the board if you need more than two simultaneous keys and it cannot do it.
2It stops at exactly six
On the test:Six keys light together, the seventh does not.
Recognise this as the standard USB HID limit, which is correct behaviour.
Enable NKRO in your keyboard firmware if the board supports it.
Try a direct USB port. Some hubs and KVM switches force 6-key boot protocol even on NKRO boards.
3A key I did not press lights up
On the test:A third cap turns green without being touched.
This is true ghosting, which is rare on modern boards.
Repeat with the same three keys to confirm it is reproducible.
Try the same combination on a second computer to rule out software.
Replace the board. Missing diodes cannot be fixed without rewiring the matrix.
4It only fails on one specific combination
On the test:Most combinations work, one particular set drops a key.
Expect this. Blocking depends on which rows and columns those specific keys share.
Remap one of the affected keys to a different physical position, if your firmware allows it.
Rebind the combination in the game or application instead, which is usually faster.
Frequently asked questions
What is keyboard ghosting?
Strictly, it is the keyboard reporting a key you never pressed, because its matrix cannot resolve which combination you meant. In everyday use the word usually describes the more common problem: a board silently dropping the third or fourth key you hold at once.
How do I test for ghosting?
Hold several keys down together and watch which stay lit on the board above. Start with three adjacent keys, then add a fourth and fifth. Any key you are holding that goes dark has been dropped, and any key that lights up unpressed is true ghosting.
What is n-key rollover?
The ability to report every key you press at once, with no limit. Standard USB keyboards report six keys plus modifiers per packet, so six-key rollover is common; n-key rollover boards work around that limit and need no special driver.
Do modifiers count toward the rollover limit?
No. Ctrl, Shift, Alt and the Windows or Command keys are reported in a separate part of the USB packet, so you can typically hold all of them plus six ordinary keys even on a six-key rollover board.
Is my keyboard broken if keys drop when I hold several?
Almost certainly not. It is a design limit rather than a fault, and it is normal on membrane keyboards and on many mechanical ones. It only matters if a combination you actually need is among the ones that fail.
Test another keyboard
Every layout below opens with its own board ready to test.
