Scroll Test
Roll the wheel over the panel. Every notch is counted by direction, and the skip check catches a wheel that jumps the wrong way.
Hover here and scroll
Choose a skip check to hunt for a faulty encoder.
What the results mean
On a notched wheel, each click you feel should produce exactly one event in the direction you turned. A few wrong-way events while scrolling in one direction is the classic sign of a worn or dirty encoder: the part that turns wheel rotation into signals. It shows up in games as weapon switching that jumps back, or in documents as a page that twitches.
Before replacing the mouse, blow compressed air around the wheel while spinning it, and check your mouse software for a scroll smoothing option that might be disguising the problem. Then check the rest of the mouse on the mouse test.
Questions
How do I test my scroll wheel?
Hover over the test area and scroll. Every wheel event is counted by direction. To check for skipping, pick "Only down" and scroll steadily downward: any event that comes through as up is flagged as a skip.
Why does my scroll wheel jump the wrong way?
Most mouse wheels use a mechanical encoder. Dust or wear makes its contacts misread, so a notch down can register as up. Compressed air or a replacement encoder usually fixes it.
What is a notched vs smooth wheel?
A notched wheel sends one event per click you feel. Smooth or free-spinning wheels and touchpads send many small pixel events. The test shows which kind your device reports.