Mouse Scroll Test

What problems this mouse scroll test tool can detect

The analyzer above was built specifically to catch the kinds of faults that a plain scroll counter or arrow-key test cannot see.

• Direction reversalsEvents that fire in the opposite direction while you're scrolling steadily one way. The number-one sign of a worn encoder and the core signal the Reversals readout tracks.
• Wheel jumpingPages leap up when you scroll down, or vice versa, caused by short bursts of reverse events. Visible in the trace as sharp "V" shapes.
• JitterThe wheel fires the right direction but with wildly uneven step sizes — a symptom of dirty optical slots or a loose contact.
• Dead zonesPositions on the wheel where no events fire at all, usually from physical damage to the encoder disc.
• Abnormal scroll ratesEither too few events for the amount of rotation, or too many, indicating driver or hardware issues.

If any of these show up while you run the mouse scroll test, the signal is clear enough to act on — whether that means cleaning the wheel, reseating the USB receiver, or buying a replacement.

How a mouse scroll test works

When you turn a mouse wheel, the browser fires wheel events that carry both a direction and a magnitude. In a healthy mouse, every tick in one direction produces an event with the same sign. In a failing mouse, the encoder disc — or the optical sensor above it — starts emitting stray pulses, and the browser sees events going the opposite way.

A good mouse scroll test should make those stray events visible, not bury them inside a counter that increments too fast to read. This page plots every wheel event as a continuous trace: steady scrolling produces a clean single-color line, and spurious reverse events interrupt it with the opposite color, so a single misread tick is impossible to miss.

How to run the mouse scroll test

The whole procedure takes about fifteen seconds.

1. Hover your cursor over the analyzer panel at the top of the page. The Sensor LED lights up green to confirm input is being captured.
2. Scroll in one direction — down or up, your choice — for ten to fifteen seconds. Use a pace slightly faster than your normal browsing rhythm, but don't push the wheel to its limit; both extremes can distort the result. Avoid deliberately reversing direction — the test is designed to catch reversals you didn't make.
3. Watch the trace. A healthy wheel draws one continuous color; a faulty one sprinkles in segments of the opposite color.

How to read your mouse scroll test results

Four readouts sit below the analyzer. Only one of them actually matters for diagnosis, but the others give context.

• EventsA running count of every wheel event the browser has captured. Useful only as a sanity check that input is registering.
• RateEvents per second over the last one-second window. A standard hardware wheel on Windows reports between 5 and 20 events per second at comfortable speed; trackpads and high-resolution wheels report far more.
• ReversalsThe metric that matters most. Zero during single-direction scrolling means the wheel is healthy. Anything above zero means the hardware is sending spurious events. More than a few per second almost certainly indicates a failing encoder.
• Last ΔYThe raw pixel delta of the most recent event — handy for spotting abnormally large or fractional values that hint at driver problems.

Common scroll wheel problems and what they look like

Beyond the general mouse scroll test above, these are the four failure modes worth recognizing on sight.

• Ghost scrollingThe wheel appears to scroll the wrong way for no reason. In the analyzer: short segments of the opposite color interrupting an otherwise consistent trace. The classic encoder-wear symptom, often fixable with compressed air if caught early. See also the ghost scroll test.
• Wheel jumpingPages lurch up and down instead of scrolling smoothly. In the analyzer: sharp "V" shapes where the direction flips and returns almost immediately. Dedicated diagnostic available on the scroll wheel jump test page.
• JitterInconsistent scroll speed without full reversal. In the analyzer: uneven spacing between points even when Reversals stays at zero. The mouse wheel jitter test focuses on this pattern specifically.
• Dead spotsSections of wheel rotation that produce no events. In the analyzer: flat stretches where the trace stops advancing despite visible wheel movement. Run the mouse wheel dead spot test for a focused diagnosis.

Mouse scroll test — frequently asked questions