Scroll Test — Check Your Mouse Wheel.
Roll your scroll wheel over the panel and watch every notch appear on a live graph, counted up and down. A clean wheel makes even, regular steps; a failing one skips, stutters, or scrolls the wrong way. This is the fast way to see exactly what your wheel is sending.
Scroll to check
Scroll up and down over this panel
Online scroll test.
Each roll of the wheel is a notch. The graph plots its size and direction so uneven or skipped steps stand out.
Read your wheel correctly
- Scroll slowly, one notch at a timeDeliberate single clicks of the wheel show each step clearly on the graph. A fast spin blurs individual notches together and hides small faults.
- Test both directionsWheels can fail in one direction only. Scroll up and down several times and compare the two notch counts — they should climb evenly.
- Watch for bars that jump sizeHealthy notches are all about the same height. One that's suddenly double or triple, or a gap where nothing registered, is a skipping wheel encoder.
- Know your device sends different deltasA mouse wheel sends chunky, discrete steps; a trackpad or free-spin wheel sends a stream of tiny values. Both are normal — the pattern is what matters.
How to use the scroll test
- 1Hover over the panel and scroll. Roll the wheel up and down; each notch drops a bar onto the graph — above the line for up, below for down.
- 2Watch the counts and the step size. Up and down notch counts should rise smoothly, and the Typical step tells you the normal size of one click of your wheel.
- 3Look for skips and stutters. A missing bar, a double-height spike, or a wildly uneven pattern flags a failing wheel encoder — the Wheel health readout calls it out.
- 4Check direction. If scrolling up registers as down, natural/reverse scrolling is enabled in your OS. Confirm the physical wheel and its click work on the mouse test.
How the scroll test works
Every time you move the wheel, the browser fires a wheel event carrying a deltaY value: negative when you scroll up, positive when you scroll down, and larger in magnitude the more you moved. This test reads each event, tallies it as an up or down notch, records the delta, and plots it as a bar so you can see the size and direction of every single step your wheel produces.
The size of that delta depends on your device and browser through the event's deltaMode: mice usually report in pixels (often around 100 per notch in Chromium) or lines (a few "lines" per notch in Firefox), while trackpads and free-spinning wheels stream many tiny pixel values for smooth scrolling. None of those is wrong — a good wheel just produces a consistent, repeating pattern. This tool learns your typical step size and flags any event that deviates sharply, which is the signature of a skipped or bouncing notch.
Two things people mistake for faults aren't. First, reverse (natural) scrolling flips the sign of the delta — if up feels like down, that's an OS setting, not broken hardware. Second, a wheel with a free-spin mode sends a long tail of decreasing deltas as it coasts; that's the flywheel, working as designed. A genuine fault looks like irregular, jumpy, or missing steps during slow, deliberate scrolling.
When to run a scroll test
The page jumps when scrolling
A wheel that scrolls up when you go down, or leaps several lines at once, shows up here as reversed or oversized deltas.
Scrolling feels notchy or skips
Missing or uneven bars during a slow scroll point to a worn or dusty encoder inside the wheel.
New mouse check
Confirm both scroll directions register cleanly and evenly before you rely on a new mouse.
After cleaning the wheel
Blew out dust or re-greased the encoder? Re-run to confirm the steps are even again.
Comparing mouse vs trackpad
See the difference between a mouse's discrete notches and a trackpad's smooth pixel stream on the same graph.
Diagnosing "natural scrolling"
Not sure why scrolling feels backwards? The direction readout confirms whether reverse scrolling is enabled.
Scroll test glossary
- Notch
- One click or step of the scroll wheel. This test counts each wheel event as a notch and plots its size.
- deltaY
- The wheel event's vertical scroll amount: negative for up, positive for down. Its size reflects how far you scrolled.
- deltaMode
- The unit of the delta: 0 for pixels, 1 for lines, 2 for pages. It differs by device and browser.
- Encoder
- The component inside the wheel that turns rotation into electrical steps. Wear or dust here causes skips and stutter.
- Free-spin
- A wheel mode that disengages the notches so it spins freely, sending a long tail of coasting deltas.
- Natural scrolling
- An OS setting that inverts scroll direction so content follows your fingers. It flips the delta sign — a preference, not a fault.
Frequently asked questions
How do I know if my scroll wheel is broken?
Scroll slowly over the panel, one notch at a time, and watch the graph. A healthy wheel drops evenly sized bars in a steady rhythm and the up/down counts climb smoothly. A failing wheel shows the tell-tale signs: bars that suddenly jump in size, gaps where a notch didn't register, or scrolling that jumps direction. If the Wheel health readout says "uneven or skipped steps" during a slow, careful scroll, the encoder is likely worn or dirty.
Why does scrolling up register as down?
That's reverse (natural) scrolling, an operating-system setting rather than a hardware fault. Natural scrolling inverts the direction so on-screen content moves with your fingers, like on a phone — it flips the sign of the wheel's delta. Turn it off in your mouse or trackpad settings if you prefer the traditional direction. The wheel itself is working fine.
My wheel skips or jumps a few lines at once. Can I fix it?
Often, yes. Skipping usually means dust or wear in the wheel's encoder. Try blowing compressed air into the wheel area, and if you're comfortable opening the mouse, the encoder can be cleaned or replaced cheaply. Some skipping is also software: check that no "smooth scrolling" or mouse utility is interfering. Re-run this test after each change to confirm the steps are even again.
Why are my scroll deltas different from someone else's?
Because delta size depends on your device and browser. A standard mouse wheel in Chrome often reports about 100 pixels per notch; Firefox may report in lines instead (a delta of just a few); trackpads and free-spin wheels send a stream of small pixel values. All are normal. What matters isn't the exact number but whether your own steps are consistent and repeatable.
Can this test check horizontal scrolling or the tilt wheel?
This panel focuses on vertical scrolling (deltaY), which is what most wheels and diagnostics care about. Horizontal tilt-wheel scrolling fires a deltaX value that this graph doesn't plot, though many tilt actions also register as button events — you can check those on the mouse test, which lights up every button.
Does the middle-click work if scrolling does?
Not necessarily — they're separate mechanisms. The wheel's rotation uses an encoder, while pressing the wheel down uses a distinct switch, so one can fail while the other works. If scrolling is fine but middle-click does nothing, test the click specifically on the mouse test, where a middle press lights the wheel region as button 1.