Mouse Scroll Wheel Tester

A faulty scroll wheel can jump, skip steps or briefly scroll the wrong way. This scroll tester records every wheel event, shows direction and running totals, and counts reversals so you can see if the wheel behaves consistently.

How to use the Scroll Tester

Move the pointer over the test area.
Scroll slowly in one direction, one notch at a time.
Scroll in the opposite direction and watch for unexpected reversals.
Compare totals after a fixed number of notches.

Understanding your results

Direction changes you did not make suggest a dirty or worn wheel encoder. Event magnitudes vary by device, browser and operating system, so compare results from the same setup rather than against another computer.

Trackpads and tilt wheels can also report horizontal scrolling.

Worked example: reading scroll totals

Scroll ten notches downward, one at a time. The running total should grow steadily, and every event should point the same way. Then scroll ten notches back up. The total should return close to where it started, and the tool should count no direction changes you did not make.

If the direction counter shows an upward event while you were scrolling down, that is a reversal. One reversal in a very fast flick is worth noting. Reversals that appear repeatedly during slow, careful scrolling suggest a dirty or worn wheel encoder.

Event sizes differ between systems, so do not worry if the numbers are not the same as on another computer. What matters is that the pattern is steady and the direction is consistent.

Fixing a jumpy scroll wheel

Clean the wheel area. Dust and debris around the wheel are a common cause of skipping. Compressed air can help.
Test in another browser. A browser smoothing setting can change how scrolling feels, even when the wheel is fine.
Check mouse software. Some tools add smoothing or acceleration to the wheel. Turn those off and test again.
Try another computer. If the problem moves with the mouse, the encoder may be worn.
Free-spinning wheels behave differently. They report many events from a single flick, so test slow, single-notch scrolls to check consistency.

For a full check of your hardware, also run the mouse tester and the button tester. If the cursor itself feels wrong, the Windows DPI guide and the Mac DPI guide explain the system settings.

Scroll Tester FAQ

Why does my scroll wheel jump?

Dust, wear in the wheel encoder or a driver smoothing setting can cause jumps. Clean the wheel area and test again.