Three terms worth separating
- Rollover
- The number or pattern of simultaneous keys the keyboard can report correctly.
- Blocking
- An intended key is not reported because of a limitation in the keyboard matrix or processing path.
- Ghosting
- An unintended key appears when a particular combination is pressed. Modern keyboards often prevent ghosting by blocking a conflicting input instead.
Build a practical test list
Write down combinations that matter in your actual work or games. Examples include W + A + Shift + Space, several rhythm-game lanes, or a design shortcut with modifiers. Reserved operating-system shortcuts are poor test cases because the page may never receive them.
Test each combination
- Start the Keyboard Check Lab tester.
- Press and hold the combination slowly, one key at a time.
- Confirm each expected key appears in the held-key list and no extra key appears.
- Release every key, then repeat in a different order.
- Repeat the same combination in another browser before treating a mismatch as hardware evidence.
Why a peak number is not an NKRO certificate
A peak of six means the browser saw six keys during that test. It does not prove that every six-key combination works, and a higher peak does not prove full N-key rollover. Matrix behavior can vary by key location and connection mode.
When replacement makes sense
Consider another keyboard only when a combination essential to your workflow fails consistently, firmware and connection checks do not help, and the manufacturer confirms the observed limitation. Marketing labels should not outweigh a reproducible test of the keys you actually need.