Keyboard ghosting test
Have you ever tried to press three or four keys at once in a game and noticed one of them simply didn't respond? That'sghosting, and it comes from the keyboard's internal matrix. This guide explains what it is, how to test for it, and how to interpret the result using theonline keyboard tester.
What is ghosting
Most keyboards use an internal matrix to wire all keys with fewer electrical traces than there are keys. That cost-saving measure has a side effect: certain combinations of keys produce identical electrical signals at the controller, and the keyboard cannot distinguish them. The result is that one or more keys simply aren't reported to the system. This behaviour is calledghosting or jamming.
What is rollover
Rollover is the maximum number of keys a keyboard can register at once without dropping any. Common values are:
- 2KRO (2-key rollover): registers up to two keys simultaneously. The bare minimum.
- 6KRO (6-key rollover): enough for most games.
- NKRO (N-key rollover): registers every key without limit, via USB Report protocol.
How to test in practice
Open the keyboard tester and enableAnti-ghosting mode. Press several keys at once — for example, three keys on the home row and a modifier (Shift or Ctrl). Watch the simultaneous counter and which keys appear as pressed. If one consistently fails on a specific combination, that's the keyboard's physical limit.
How to reduce ghosting impact
- Reorganise shortcuts to avoid problematic combinations (W + Shift + Space, for example).
- Use an NKRO keyboard if your workflow relies on many simultaneous keys.
- Configure the system to use USB Report protocol instead of Boot protocol.
- Consider swapping Ctrl for Shift in shortcuts that need more modifiers.
Frequently asked questions
What is N-Key Rollover (NKRO)?
It is the ability of a keyboard to register every pressed key simultaneously without dropping any. NKRO keyboards usually have an electrical matrix that isolates each key.
Is anti-ghosting the same as rollover?
They are complementary. Anti-ghosting is a matrix technique to avoid ghost keys; rollover is the maximum number of keys a keyboard reports correctly at once. A keyboard can have 6-key rollover with anti-ghosting on certain combinations, for example.
Why does my gaming keyboard only register three keys?
It usually happens because the system uses USB Boot protocol, which limits how many keys are reported per polling cycle. Switching to USB Report protocol or using a dedicated USB port typically fixes it.