How to use the ghosting test
- Click the test box so Space and the arrow keys don’t scroll the page.
- Pick a gaming combo, or just press and hold any keys you like.
- Add one key at a time and keep holding the others. Each key you hold should appear.
- If you’re holding a key and it doesn’t appear, your keyboard blocked it. If a key you didn’t press appears, that’s ghosting.
- Keep adding keys until the count stops going up. “Most at once” keeps your best result until you press Reset.
Skip combos with Ctrl or Command. Browsers keep shortcuts like Ctrl + W (close tab) for themselves, and the test doesn’t block them.
Ghosting, blocking and key rollover
Most keyboards don’t wire every key separately. The keys sit in a grid of rows and columns, called a key matrix, and the controller scans it to see which ones are closed.
- Ghosting is a key you didn’t press showing up. If you hold three keys at three corners of a rectangle in the grid, current can flow to the fourth corner, and the controller sees a fourth key.
- Blocking, also called jamming, is how most keyboards stop ghosting: they ignore any key that could be a ghost. So the usual symptom is a key you’re holding that doesn’t register.
- Key rollover is how many keys a keyboard guarantees to register at once, whichever keys they are.
Keyboards with a diode on every key don’t ghost, because current can only flow one way through each key. That’s one common way keyboards reach NKRO.
| Rollover | What it means | What you’ll see in the test |
|---|---|---|
| 2KRO | Any 2 keys always register. A third may or may not, depending on the keys. | Some 3- and 4-key combos lose a key |
| 6KRO | Any 6 regular keys always register, plus the 8 modifier keys. | The count stops at 6 regular keys, plus Ctrl, Shift, Alt and Win |
| NKRO | Every key registers, however many you hold. | As many keys as your fingers can hold, if the system passes them on |
The 6-key USB limit
The USB HID specification defines a simple “boot protocol” keyboard report so keyboards work in a BIOS before any driver loads. That report has room for 6 regular keys plus 8 modifier bits: left and right Ctrl, Shift, Alt and Win or Command. A keyboard using it can’t report a seventh regular key at the same time.
NKRO keyboards send a different report to get around this. Many let you choose between 6KRO and NKRO in their software or with a key combo, and some drop back to 6KRO in a BIOS. The eight-key “A S D F J K L ;” preset shows straight away which mode you’re in.
Why the browser may show fewer keys
The test can only show what the operating system and browser pass on, so a missing key isn’t always the keyboard’s fault.
- System shortcuts. Combos with the Windows or Command key, or Alt + Tab, go to the operating system.
- macOS and Command. While Command is held, macOS doesn’t report other keys being released. The test clears all held keys when you let go of Command.
- Shift and the numpad on Windows. With Num Lock on, Shift plus a numpad key can make Windows report Shift as released.
- Switching windows. If the browser loses focus, it stops receiving keys, so the test clears what you were holding.
To check that every single key works, use the keyboard test. You can also measure your typing speed, your actions per minute or how fast you can hit the spacebar.