Rollover and ghosting explained
Key rollover is how many keys a keyboard can report at the same time. Inside most keyboards the switches sit on a grid of rows and columns (the matrix). Pressing several keys at once can make the controller unable to tell which keys are really down, so cheaper designs simply stop accepting new keys after a few.
- 2KRO / 3KRO — only two or three keys are guaranteed in any combination. Common on older and budget keyboards and some laptops.
- 6KRO — six regular keys plus all modifiers. This is the limit of the standard USB “boot” keyboard report, used by many keyboards and most BIOS screens.
- NKRO (n-key rollover) — every key is reported independently, no matter how many you hold. Usually needs diodes on each switch and a USB or 2.4 GHz connection.
Ghosting is the matrix failure mode: hold three keys that form a rectangle on the grid and a fourth, unpressed key can appear. Most modern keyboards prevent this by blocking the extra key instead — that is what “anti-ghosting” usually means. Blocking shows up here as a key that stays dark while you hold it.
Reading the result
- 7 or more regular keys at once: beyond the 6-key USB limit, so the keyboard very likely supports NKRO.
- Exactly 6 regular keys: if a 7th key you were holding stayed dark, the keyboard (or its current mode) is 6KRO. That is plenty for typing and most games.
- 3–5 keys, or a combo that fails: limited rollover. Gaming combinations such as W + A + Shift + Space can drop inputs.
- A red key you didn't press: ghosting — the matrix reported a phantom key.
How to run the rollover test
- Start with Free test: lay your fingers flat and press keys one by one without releasing any.
- Watch Held now. When a newly pressed key stays dark, you have found the limit.
- Pick a preset combo, such as WASD + Shift + Space, and hold every highlighted key together.
- Try a few different areas of the keyboard — rollover limits often depend on which keys share a matrix row or column.
Method and limits
The test tracks every key-down and key-up event by physical KeyboardEvent.code and counts the keys currently held, separating regular keys from modifiers. It can only count what the operating system passes to the browser:
- Some combinations trigger OS shortcuts and are swallowed, such as Alt + Tab, Win + letter keys or ⌘ + Space. Combinations with Ctrl or ⌘ are passed to the browser so its shortcuts keep working, so avoid them here.
- On macOS, keys released while ⌘ is held don't send a release event; the test releases them when ⌘ goes up.
- Bluetooth keyboards, USB hubs, KVM switches and BIOS-compatibility modes can force 6KRO even on an NKRO keyboard.
Typical rollover by connection
| Keyboard / connection | Typical rollover | Notes |
|---|---|---|
| USB, standard (boot protocol) | 6 keys + modifiers | Works everywhere, including BIOS screens. |
| USB gaming / mechanical with NKRO | All keys | Some need an NKRO toggle (often an Fn shortcut) or software setting. |
| 2.4 GHz wireless dongle | Varies, often NKRO | Depends on the model's firmware. |
| Bluetooth | Often 6 keys | Many Bluetooth keyboards use a 6-key report. |
| Laptop built-in | Varies | Often limited, with certain combinations blocked. |
Getting more keys to register
- Switch the keyboard to NKRO mode in its software or with its documented Fn shortcut.
- Connect directly to the computer, not through a hub, monitor USB port or KVM switch.
- Use the cable or 2.4 GHz dongle instead of Bluetooth.
- For games, rebind actions so frequent combinations don't share a matrix row or column that blocks.
Frequently asked questions
What does NKRO mean?
N-key rollover: the keyboard reports every key independently, so any number of simultaneously held keys registers correctly. It is common on mechanical and gaming keyboards.
Is 6-key rollover enough for gaming?
For almost every game, yes. 6KRO means six regular keys plus all modifiers at once. Rhythm games, stenography and some fighting-game inputs are the main cases where NKRO helps.
Why do some combinations work and others don't?
Without full NKRO, the limit depends on how the keys are wired in the matrix. Keys that share a row or column with other held keys are blocked first, so the same number of keys can pass in one area and fail in another.
What is the difference between ghosting and blocking?
Ghosting adds a key you never pressed; blocking ignores a key you did press. Modern keyboards almost always block instead of ghosting, which is safer but still drops inputs.
Why does my keyboard show fewer keys over Bluetooth?
Many keyboards send a 6-key report over Bluetooth even if they support NKRO over USB. Test again with the cable or wireless dongle.
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