What Ghosting Is
Microsoft defines ghosting as some keys not working when several keys are pressed at the same time. Logitech says it usually shows up with three or more keys held together.
Logitech gives an example: type "XML" fast, without letting go of X before pressing M and L. On an affected keyboard, only X and L appear.
Ghosting is not the same as a dead key. A dead key fails every time. A ghosted key works on its own and drops out only in certain combinations.
Run the Test
- Open the keyboard test. The test area is ready as soon as the page loads.
- Press each key you plan to test on its own first, so you know it works.
- Hold the keys you use together in games or shortcuts, one at a time, without letting go.
- Watch which keys light up, and the Most Keys at Once counter. It shows the largest number of keys the page saw held at the same moment.
- Repeat with other combinations. Ghosting depends on which keys you press, so one combination passing doesn't clear the whole keyboard.
If the counter stops climbing and the newest key stays dark, that combination ghosts. Write it down, because the fix may be as small as moving one game binding.
Why It Happens
Microsoft names three causes. The keyboard's hardware can't read the combination. The software on the computer doesn't support that many keys at once. Or the connection between them limits how many keys are reported.
Microsoft explains that most keyboards detect keys with a grid of row and column wires. With three keys held in certain positions, the pattern on the grid can match more than one set of keys. The keyboard then can't tell which keys are held.
The connection sets a ceiling too. Microsoft says the standard USB reporting protocol limits a keyboard to six regular keys at once, plus modifiers such as Shift, Ctrl, and Alt.
Read the Result
- Stops at 2 or 3 keys for some combinations: those keys block each other on the keyboard's grid. That is hardware ghosting.
- Stops at 6 regular keys whatever you press: the keyboard is likely working within the standard USB report limit.
- Every key you hold lights up: the keyboard has no ghosting on that combination.
- Some keys never light up, even alone: that is a different fault. The page can't see keys such as Fn, and the system handles the Windows key and some shortcuts before the browser does.
Logitech notes that two modifier keys with one regular key should still work, such as Ctrl, Shift, and a letter. That holds even on its membrane keyboards that can ghost.
What to Do About It
- Change the combination: move a game binding to a key that doesn't ghost with the others, then test again.
- Use modifiers where you can, since two modifiers and one regular key still work on keyboards that ghost.
- If the browser test passes but a game still drops keys, the cause may be the software, one of the three causes Microsoft lists. Check the game's own settings.
- Logitech lists the Signature K650, Craft, MX Keys, and K860 as membrane keyboards that can ghost. It suggests a mechanical keyboard if this matters to you.
- When buying, look for anti-ghosting or N-key rollover in the specs, then check the result with the keyboard test when it arrives.