Mouse Scroll Wheel Test
To test a scroll wheel, point at the scroll box and roll the wheel slowly one way. Each notch should add one to the same counter. If the opposite counter jumps up while you scroll one way, the wheel is skipping, which usually means a dirty or worn encoder. Then test the other direction and any sideways tilt.
How it works
Point at the grey box and use your mouse there. The page reads your browser’s mouse events and never sends them anywhere.
These tests need JavaScript. The explanations below work without it.
Made for a real mouse. On a phone or tablet, only the click speed test works with touch. In Firefox and Safari a side button may still go back a page; the page tries to stop that.
Scroll wheel test
Scroll here. The page will not move while the pointer is in this box.
How to do it
- Point at the scroll box.
- Roll the wheel slowly down five notches and check only the Down counter rises.
- Roll up five notches and check only Up rises.
- Tilt the wheel sideways if your mouse supports it.
- Look at the wrong-way jumps counter.
How to fix a scroll wheel that skips
- Blow compressed air into the gaps around the wheel while rolling it.
- Check that smooth scrolling or a "free spin" mode is not making it feel wrong.
- Try another USB port or a fresh battery.
- If it still jumps, the wheel encoder may be worn. Contact the maker if it is under warranty.
The delta unit shows how your browser reports the wheel: in pixels (most common), lines or pages. It does not mean anything is wrong.
Frequently asked questions
Why does my scroll wheel jump up when I scroll down?
Dust in the wheel encoder or a worn encoder can send a single step the wrong way. The test counts these as wrong-way jumps. Cleaning with compressed air often helps; if not, the encoder needs replacing.
How do I test horizontal scrolling?
Tilt the wheel left and right, or hold Shift and scroll on some systems. The left and right counters should go up. Many basic mice have no horizontal scrolling at all, which is normal.
Why does one notch count as several events?
Some mice, touchpads and smooth-scrolling settings split one movement into several small events. Watch whether every event goes in the same direction while you scroll one way; that matters much more than the exact count.
Will the page scroll during the test?
No. While the pointer is over the scroll box, the page stops the wheel from scrolling the page so you can count steps. Move the pointer outside the box to scroll the page again.
Does this work with a touchpad?
Yes. Two-finger scrolling on a touchpad sends the same wheel events, so the counters work. Touchpads send many small steps, so the counts will be much higher than with a mouse wheel.
Last updated: October 13, 2026