Key Rollover (NKRO) is a free device test tool that runs entirely in your browser — see every key you hold at once. No upload, no account, no limits.
See exactly which keys your keyboard reports while you hold several at once. Each pressed key lights up on the on-screen layout, and the tool tracks the most keys held simultaneously plus every distinct key it has seen.
It's a quick way to probe rollover and ghosting: hold six or more keys and watch whether they all register, or whether some drop out at your keyboard's limit.
Either your keyboard hardware caps simultaneous keys (common on membrane boards), or the browser/OS reserved that combo. The on-screen maximum is therefore a floor, not the hardware's true spec.
The test box calls preventDefault so combos like Ctrl+W don't act on the page while you test them.
Every calculation happens on this page, in your own browser. Your input is never sent to a server, never logged and never used for training — which also means the tool keeps working when you are offline.