Key Rollover / Ghosting Test
Find how many keys your keyboard reports at once — and why six is not a fault.
Click here, then hold down as many keys as you can at the same time
Modifier keys are shown in amber — they are carried separately and do not count toward the six.
How this test works
You hold down as many keys as you can reach simultaneously, and the page records the largest set that registered together. Modifiers are counted separately from ordinary keys because the USB HID report carries them separately: Ctrl, Shift, Alt and the Windows or Command key live in their own byte and never consume one of the six ordinary slots. That six is the number worth understanding. It is the capacity of the USB HID boot protocol, which nearly every keyboard uses, and hitting it means the protocol filled up rather than the keyboard failing. Keyboards advertising N-key rollover negotiate a different report format to get past it. The tool reports which of those you have and declines to call either one broken.
What the results mean
- N-key rollover
- More than six ordinary keys at once. The keyboard is using a report format that carries every key independently.
- 6-key rollover
- Exactly six. The USB HID boot protocol limit — the standard behaviour, not a fault.
- Modifiers held alongside
- Ctrl, Shift, Alt and Meta. Carried separately by the protocol, so they never eat into the six.
- Fewer than six
- Usually the grip or a browser intercept rather than the keyboard. Genuine matrix blocking affects specific combinations, so a different group of keys reaches further.
Common problems and fixes
- It stops at six keys — is my keyboard bad?
- No. Six is what the USB HID boot protocol carries, and the great majority of keyboards use it. It is a specification, not a defect.
- I can only get three or four keys
- Try keys spread widely across the board rather than clustered together. Matrix blocking affects particular combinations, and clustered keys often share wiring.
- Some combinations do nothing at all
- The browser or the operating system took them first. Anything involving Tab, the Windows or Command key, or the function row is frequently intercepted before a page sees it.
Frequently asked questions
What is the difference between ghosting and blocking?
Ghosting is a phantom keypress the keyboard reports that you did not make — genuinely rare on any board with diodes in the matrix. Blocking is the keyboard refusing to report an additional key. Most pages using the word ghosting are describing blocking or the protocol limit.
Do I need N-key rollover?
For typing, no — six keys plus modifiers is far more than typing ever needs. It matters in games where several movement, action and modifier keys are held at once, which is the case it was invented for.
Why do modifier keys not count toward the six?
Because the USB HID keyboard report puts them in a dedicated byte, one bit each, separate from the six slots for ordinary keys. That is why you can hold Ctrl, Shift and Alt together with six other keys.