Mouse Scroll Test
Scroll your wheel and watch each event appear with its direction, delta value, and the deltaMode unit. The test counts total up and down steps this session and shows the deltaMode meaning (0 = pixels, 1 = lines, 2 = pages). Runs locally, no data leaves your device.
Nothing you scroll leaves this tab. No storage, no network requests. Refresh clears the session.
Scroll with your mouse wheel inside this area
- Down
- 0
- Up
- 0
- Events
- 0
- Mode
- —
Last event
- deltaY
- —
- deltaX
- —
- Direction
- —
- deltaMode
- —
- Dominant axis
- —
The scroll unit depends on the browser's deltaMode — compare like with like.
What this measures
- Wheel direction per event (up or down).
- Delta value per wheel event as the browser reports it.
- Total up steps and total down steps this session.
- The deltaMode of the last event: 0 = pixels, 1 = lines, 2 = pages — with a note that the unit depends on deltaMode.
What this cannot measure
- Hardware scroll switch faults versus OS or browser interpretation — the test shows what the browser delivered.
- Free-spin versus ratcheted mode — the test reports events received; more events per notch is not a fault.
- Smooth-scrolling interpolation done by the OS or browser after the wheel event.
- Horizontal scroll (tilt wheel) as a primary axis — if the wheel tilts, deltaX events are reported; the test mentions the dominant axis honestly.
How to get a steady reading
- Scroll slowly, one notch at a time, to verify single-step counting.
- Scroll fast to check for skipped steps — the browser may coalesce rapid events.
- Compare up and down symmetry — the step counts should be similar for the same physical movement.
- Test in the same browser when comparing mice — deltaMode varies by browser and OS.
How to read the results
| Metric | What it means |
|---|---|
| Direction | Up or down for each wheel event. |
| Delta | The raw delta value the browser reported for that event. |
| Steps | Running count of wheel events in each direction this session. |
| Totals | Total up steps and total down steps at the end of the session. |
| deltaMode | 0 = pixels, 1 = lines, 2 = pages. The same physical wheel movement reports different numbers depending on this unit. |
Why the scroll unit varies (deltaMode)
The WheelEvent.deltaMode property tells you the unit of deltaX, deltaY, and deltaZ. A value of 0 means pixels, 1 means lines, 2 means pages. The same physical notch on a ratcheted wheel can report a delta of 100 in pixels (deltaMode 0), 3 in lines (deltaMode 1), or a fraction of a page (deltaMode 2) depending on the browser and OS settings. Windows often uses lines; macOS often uses pixels. The test shows the deltaMode so you can compare like with like — do not compare a pixel-mode number to a line-mode number.
Notched versus smooth wheels
A ratcheted (notched) wheel typically sends one event per notch. A free-spin or smooth wheel may send many events per revolution, especially when spun fast. More events per unit of movement is not a fault — it is how that wheel reports. The test counts what the browser delivers. If you switch from a notched to a smooth wheel, expect higher step counts for the same visual scroll distance.
Skipped-step honesty
If you scroll fast and the test reports fewer events than you expect, the browser may have coalesced multiple wheel events into fewer deliveries. This is a browser delivery observation, not a wheel fault. The test shows what arrived. Compare browsers on the same mouse to see how coalescing differs.
Privacy
This test runs entirely in your browser tab. No scroll data is sent anywhere. No history is stored. Refreshing the page clears the session. You can verify this in DevTools: open the Network tab, scroll, and confirm no requests fire.
Frequently asked questions
Why do my scroll numbers differ between browsers?
Different browsers and operating systems use different deltaMode units (pixels, lines, or pages). The same physical wheel movement produces different delta values in each unit. The test shows the deltaMode so you know which unit you are looking at. Compare the same mouse in the same browser for consistent numbers.
Does more steps mean a better wheel?
Not necessarily. A free-spin wheel sends more events per revolution than a notched wheel. A browser that does not coalesce events shows more steps than one that does. More steps means the browser delivered more events — it does not rank wheel quality.
Can this test a faulty scroll wheel?
It shows what the browser received. If a notch produces no event, the browser did not get one — that is the finding. It could be a hardware fault, a driver issue, or the browser coalescing events. Test the same mouse in another browser or on another computer to narrow the cause.
Does horizontal scroll work?
If your wheel tilts left/right or you have a horizontal scroll surface, the browser fires wheel events with deltaX. The test reports the dominant axis (usually deltaY for vertical). Horizontal events appear if they occur — the test does not filter them out, but the UI focuses on the primary scroll direction.
Related tests
Mouse Polling Rate Test
Live Hz, stability graph, and variation — browser-observed, not a hardware measurement.
Mouse Tests Hub
Overview of all mouse tests: polling rate, click/double-click, and scroll.
Mouse Click & Double-Click Test
Five-button registration, press counts, and possible-bounce detection — no fault verdict.
Mouse Reaction Time Test
Five-trial click latency measurement from an on-screen visual signal.
Last reviewed 2026-10-12