Key Rollover Test
Hold several keys at once to see how many your keyboard can register simultaneously.
Last key
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Code
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Keys held now
0
Max simultaneous
0
Blue = pressed right now. Green = already detected. Click this page first so it receives keyboard input.
Your test runs locally in your browser. No device data is uploaded.
How to use the key rollover test
Hold down a growing number of keys at the same time and watch the counters. The maximum simultaneous value is the highest number of keys registered together.
What this test checks
Rollover describes how many keys a keyboard can report at the same moment. Membrane keyboards often share wiring between keys, so certain combinations are dropped or misread.
Full n-key rollover keyboards report every key you hold. Six-key rollover is typical for USB gaming keyboards and is enough for almost all games.
Some keys are ignored by the operating system when many are pressed together, so test with letter clusters rather than modifier-heavy combinations.
Common key rollover problems
If pressing three keys drops one, your keyboard is ghosting. Check whether it is running in a compatibility mode, and try letters in different areas of the keyboard.
Frequently asked questions
- What is n-key rollover?
- The ability to report every key you are holding, no matter how many. A board with n-key rollover (NKRO) has no limit worth hitting; most membrane keyboards manage between two and six simultaneous keys depending on which ones they are, and stop registering anything beyond that.
- What is the difference between ghosting and rollover?
- Rollover is how many keys your board can report at once. Ghosting is the failure mode when you exceed it — either a held key stops being reported, or in older designs a key you never pressed appears. Both come from the same matrix limitation.
- How many keys should my keyboard handle?
- Six plus modifiers is the practical ceiling for anything connected as a standard USB keyboard, because that is what the basic USB HID keyboard protocol carries. Boards advertising full NKRO switch to a different reporting mode to get past it. If yours stops at two or three on ordinary letter keys, that is a low-cost membrane matrix.
- Does the result depend on which keys I press?
- Yes, and that is the most useful thing this test shows. Rollover limits follow the physical matrix, so one group of keys may handle six at once while another blocks at three. Try the combinations you actually use rather than a random handful.