Keyboard Rollover Test
Choose a combination to press at once, then hold several keys to see which key events the browser receives at the same moment, the maximum simultaneous count, and possible missing keys.
Test settings
Example: KeyQ, KeyW, KeyE. Up to 32 codes; duplicates are merged automatically.
Enter 1–32 valid KeyboardEvent.code values, such as KeyA, Space, or ShiftLeft.
Tab remains available to leave the test area. Auto-repeat events are not counted twice.
- Current concurrency
- 0
- Best match
- 0 / 6
- Last key
- —
- No keys currently held
- Current concurrency
- —
- Best match
- —
- Possible missing
- —
The result describes KeyboardEvents received by this browser. It does not replace keyboard-firmware inspection, USB capture, or laboratory hardware testing.
Expected combination and best simultaneous keys
Expected keys
- KeyW
- KeyA
- KeyS
- KeyD
- ShiftLeft
- Space
Best received together
- No combination received yet
Possible missing
- KeyW
- KeyA
- KeyS
- KeyD
- ShiftLeft
- Space
Combination count comparison
- Expected6
- Best match0
- Missing6
After testing starts, this area compares expected keys, the best simultaneous match, and keys that may still be missing.
Learn more
Method, formula, and result definition
currentKRO is the number of unique codes in the activeCodes set; maxKRO is the largest currentKRO during this round. The page keeps the simultaneous snapshot with the most expected keys received and marks the combination complete only when that snapshot contains every expected key.
Test several combinations, such as WASD+Shift+Space, QWEASD, modifier keys with the main section, and arrow keys. One passing combination proves only that this combination was observed completely at the browser-event layer during this run.
How to use and limitations
The browser cannot know which keys were physically pressed but not reported by the device. Tab, system shortcuts, Fn and media keys may not be captured; focus loss clears the current held-key set; remote desktops, virtual machines and input methods may change events. A peak above six does not mean that every combination is NKRO.
How do I test keyboard rollover?
Choose the combination you want to press at once, select Start new round, focus the test area, and hold those keys together. The page uses only keys received at the same moment and does not accumulate keys pressed in sequence.
What is the difference between 6KRO and NKRO?
6KRO generally means that six ordinary keys can be reported at the same time; NKRO indicates a higher or full-key concurrency capability. One peak or one passing combination is not proof that every combination has full rollover.
Why did the browser not receive a key I pressed?
Possible causes include keyboard-matrix conflicts, USB report limits, intercepted system shortcuts, a remote environment, or focus loss. The page can only report whether the event reached this browser.
Tool information and sources
All key events and statistics are processed only in this browser. Nothing is uploaded, no remote API is called, and nothing is written to the URL or local storage.
This tool uses no third-party runtime code or assets. The algorithm and interface are independently implemented; external links only explain browser-event and HID standards.