Keyboard Ghosting Test
Free online keyboard ghosting test. Hold the key combinations shown and the page tells you which keys your keyboard drops, whether a phantom key appears, and what rollover class you actually have.
Hold the key combinations below. The test reports three things your keyboard will never tell you on its own: which keys it drops when several are held, whether a key you never touched ever appears, and how many keys it can genuinely register at once.
Click this box, then hold the keys for step 1 below.
Modifier keys (Shift, Ctrl, Alt, the OS key) are reported separately by most keyboards and usually do not count against the rollover limit. Nothing you press leaves your device.
How to read your result
| What you saw | What it means |
|---|---|
| Every step passes and the count reaches 7 or more | Full or near-full n-key rollover. Nothing to fix. |
| Steps pass but the count stops dead on 6 | 6KRO, or an NKRO board sitting in USB boot-protocol mode. Check the manual for a rollover toggle, commonly Fn+N. |
| A key in the combination never lights up | Blocking. The keyboard refused to report the key rather than risk a ghost. Normal on membrane and laptop keyboards. |
| A key you never pressed lights up red | A genuine ghost. Repeat the step to confirm, then avoid that combination or replace the keyboard if it matters. |
| The count never passes 2 | 2KRO. Typical of cheap membrane boards; fine for typing, limiting in games. |
If a key does nothing on its own as well as in combination, this is not a rollover problem at all – see the key not working guide, or run the full keyboard tester to check every key in turn.
Why keyboards use a matrix
A full-size keyboard has around 104 switches. Giving each switch its own wire to the controller would need 104 inputs, so keyboards wire the switches into a grid instead: typically 8 rows and around 18 columns. The controller drives one row at a time and reads all the columns; a pressed switch connects its row to its column, so the controller sees which switches are down by scanning rows in sequence a few hundred to a few thousand times per second. About 26 pins cover more than 100 keys.
The saving comes with a catch. When several switches are pressed, current has more than one path through the grid. Press three keys that form three corners of a rectangle in the matrix (the same two rows and the same two columns) and current can flow from the driven row, through the first switch, along the column, through the second switch onto the other row, and through the third switch back onto a column the controller is reading. The fourth corner of the rectangle looks pressed even though nobody touched it. That phantom keypress is a ghost.
Blocking, ghosting, and diodes
Cheap keyboards handle this in firmware: when the controller detects a combination that could produce a ghost, it simply refuses to report the third key. That is called blocking or jamming, and it is why a laptop might type A and D together but drop W when you add it. The key you pressed does nothing, which is safer than a ghost but still a failure in a game. This is the fault the test above finds most often.
The proper fix is a diode in series with every switch. A diode lets current flow in one direction only, so the sneak path back through the second switch is cut off and the controller can read any combination of switches without ambiguity. Almost every mechanical keyboard has per-key diodes; almost no membrane or laptop keyboard does, because it adds 100 components to a product built to a price. Manufacturers who advertise "anti-ghosting" on a membrane board usually mean they have added diodes to the WASD block and a few common gaming keys only.
2KRO, 6KRO, and NKRO
Rollover is the number of keys a keyboard can register at once and report correctly. The number after the K is that count.
- 2KRO guarantees any two keys. Three may or may not work depending on where they fall in the matrix. Typical of basic membrane and laptop keyboards.
- 6KRO guarantees six non-modifier keys plus Shift, Ctrl, Alt, and the OS key, which are reported separately. This is the limit of the USB "boot protocol" report format, which was designed so a keyboard would work with a BIOS before any driver loaded. Many mechanical keyboards ship in this mode.
- NKRO means every key can be down at once and each one is reported. It needs per-key diodes on the hardware side and a different USB report format on the firmware side.
Anti-ghosting and rollover are related but not the same. A keyboard can have full diodes (no ghosts possible) but still be limited to reporting six keys by its USB mode. Conversely, a membrane board might promise "26-key anti-ghosting" for the gaming cluster and only 2KRO everywhere else.
Why WASD, Shift, and Space matter
The combinations that break in games are predictable, which is why they are steps 1 and 2 above. Sprinting diagonally while jumping means holding W, A, Shift, and Space at the same time, and then perhaps tapping R to reload or E to interact. On a 2KRO membrane board, W and A frequently sit in a matrix rectangle with Space or with a nearby letter, so one of them is blocked and the character stops moving or fails to jump. Shift is a modifier and does not count against rollover on most boards, but on some very cheap keyboards Shift is in the matrix like any other key and adds to the problem.
Fighting games with multi-button inputs, rhythm games where you hold chords, and emulators with two players on one keyboard push past six keys quickly, which is where 6KRO stops being enough and NKRO is worth having. For typing, spreadsheets, and shortcuts, rollover never becomes a problem, because a fast typist holds at most three keys for a few milliseconds.
The USB vs PS/2 myth
You will still read that "USB is limited to six keys, so real NKRO needs PS/2". That was true of early USB keyboards and is now wrong. PS/2 sends each keypress as its own interrupt to the computer, so it has no inherent limit. USB's boot protocol report has six slots, but a keyboard does not have to use the boot protocol once the operating system has loaded. NKRO USB keyboards send a bitmap report with one bit per key (or several boot-protocol reports on multiple endpoints), and Windows, macOS, and Linux have all understood this for many years. If your USB keyboard tops out at six, look for a mode switch; the interface is not the cause. PS/2 ports are now rare enough that the question is mostly academic.
What the test cannot tell you
The browser sees key events only after the keyboard firmware, the USB or Bluetooth link, and the operating system have all had their turn, so a few honest limits apply:
- The operating system swallows some combinations before the browser sees them – Alt+Tab, the OS key with certain letters, Ctrl+Alt+Del. A key missing from one of those is not a keyboard fault, which is why the guided steps avoid them.
- The Fn key is handled inside the keyboard and never reaches the computer at all.
- Rollover over Bluetooth is often capped at 6KRO by the wireless firmware even on a keyboard that does full NKRO over its cable. Test both if you have the option.
- A single phantom key seen once can be a stray finger. Repeat the step before believing it.
What to buy if it matters
For general use, any 6KRO keyboard with diodes is enough. For gaming, look for "NKRO" or "full N-key rollover" rather than "anti-ghosting", since the latter usually covers only a subset of keys. Be aware that some NKRO boards need a toggle to leave boot mode. If you already own the keyboard, the test above tells you what you actually have in under a minute.
Frequently asked questions
How does this page detect ghosting?
During a guided step the page knows exactly which keys you were asked to hold. If a keydown arrives for a key outside that set while you are holding the others, the keyboard reported a key you did not press, which is a genuine ghost. That is why the guided steps can detect ghosting and free-roll mode cannot: without knowing what you meant to press, no web page can tell a ghost from a typo.
What is keyboard ghosting?
Ghosting is when the keyboard reports a key you did not press. It happens on keyboards without per-key diodes when three pressed keys form three corners of a rectangle in the switch matrix; current leaks through them and the fourth corner looks pressed. Most modern keyboards block the third key instead of ghosting, which is technically blocking, but the word ghosting is used for both.
A key in the combination never lights up. Is that ghosting?
No, that is blocking, and it is far more common. The keyboard noticed that reporting the key could produce a ghost, so it refused to report it at all. It looks like a dead key but only in that particular combination; the same key works fine on its own. Both faults come from the same missing diodes.
What does NKRO mean?
N-key rollover: every key on the keyboard can be held at the same time and each one is reported correctly. It requires a diode on every switch so the matrix can be read without leakage, plus firmware that reports more than six keys at once.
Is 6KRO enough for gaming?
For almost every game, yes. Six simultaneous non-modifier keys plus all the modifiers is more than most people ever press at once, and Shift, Ctrl, and Alt do not count toward the six. Rhythm games and some fighting games can exceed it; everything else is fine.
Do I need PS/2 for NKRO?
No. PS/2 supports NKRO naturally because each keypress is sent as its own scan code, but USB keyboards have supported NKRO for well over a decade using a bitmap report format instead of the six-slot boot protocol. If your USB keyboard is limited to six keys, it is the keyboard's firmware, not USB.
Why does my keyboard stop at six keys in the test?
The keyboard is running in USB boot protocol mode, which reports at most six keys plus modifiers. Many NKRO keyboards default to this for compatibility with BIOS screens and let you switch with a key combination, commonly Fn plus N or Fn plus a function key. Check the manual.
Why can I not press W, A, and Space together on my laptop?
Laptop keyboards use a membrane matrix with no diodes and often only 2-key rollover for some combinations. The controller blocks the third key to avoid a ghost. It is a limitation of the hardware and cannot be fixed in software; a USB gaming keyboard is the workaround.
Last updated 2026-09-27. Everything on this page runs in your browser. Nothing you type or upload leaves your device.