Keyboard Ghosting Test — Check Your Key Rollover

Ghosting is when your keyboard fails to register a key you pressed because too many other keys are held at the same time. It is caused by the shared-matrix design used in most standard keyboards to reduce manufacturing cost. Gaming keyboards use diodes on each key to prevent this.

N-key rollover (NKRO) means the keyboard can register every key pressed simultaneously, no matter how many. Each key has its own dedicated electrical path to the USB controller. Most standard keyboards support 2–4 key rollover. Gaming keyboards commonly support 6KRO or full NKRO.

The test listens to the browser's keydown and keyup events. When you hold multiple keys, it counts how many are registered simultaneously. If a key you are physically holding does not appear highlighted, your keyboard is ghosting it. The test cannot detect phantom keys because they would appear as unexpected registrations.

Yes — 6KRO keyboards register up to 6 standard keys at once, plus modifier keys like Shift, Ctrl, and Alt which are typically handled on separate lines and do not count toward the rollover limit. This is sufficient for the vast majority of gaming scenarios.

The USB HID keyboard protocol has a 6-key limit per report packet for standard key codes. Modifier keys are transmitted in a separate byte, so they bypass this limit. To achieve full NKRO over USB, manufacturers use a custom driver or the USB Boot Protocol workaround. PS/2 connections have no such limit and naturally support NKRO.

Yes. The keyboard display reflects the live state of currently held keys. When you release them, the highlights clear. The maximum simultaneous count and the ghost log are preserved so you can review your results without holding keys down.