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Mouse Scroll Test

See whether browser wheel events arrive in every direction, with exact event counts and raw horizontal and vertical deltas.

Privacy: your files never leave your device. All processing happens locally in your browser.

How to use

  1. 1.Place the pointer over the dashed test area and move the wheel or trackpad vertically and horizontally.
  2. 2.Compare total events, directional buckets, the latest delta pair, and signed cumulative X and Y values.
  3. 3.Repeat under the same browser and device settings, then select Reset test to clear the local session.

About Mouse Scroll Test

Mouse Scroll Test displays the wheel events that a browser delivers while the pointer is over one visible test area. Move a mouse wheel or use a trackpad gesture inside the dashed zone. The page counts total events, classifies the dominant direction as up, down, left, right, or none, and shows the latest horizontal and vertical delta values. It also adds the raw deltas across the current session. Reset returns every count and total to zero.

The direction rule is deliberately transparent. When both deltas are zero, the event is labeled none. Otherwise, the tool compares the absolute horizontal and vertical values. A vertical value at least as large as the horizontal value becomes up or down according to its sign. A larger horizontal value becomes left or right. Equal nonzero magnitudes choose the vertical direction. This product rule gives each event one visible bucket without implying that diagonal gestures contain movement in only one axis.

Raw delta values are browser event data, not calibrated physical distance. Different browsers, operating systems, mouse drivers, wheel settings, trackpads, accessibility software, and hardware can produce different magnitudes for movements that feel similar. A delta can represent pixels, lines, pages, or another browser-defined unit depending on the event. This tool intentionally does not convert the values to centimeters, wheel notches, screen pixels traveled, or a normalized cross-device score.

The test area prevents its own normal page scrolling when it receives a wheel event. That keeps the target in place while you compare directions. Wheel gestures outside the area continue to behave normally and are not counted. The area can receive keyboard focus for a visible outline, but keyboard arrow keys are not treated as wheel input. Touch scrolling that does not generate wheel events will not appear, and a browser may combine, smooth, accelerate, or suppress events before the page sees them.

Use several short movements in each direction. A traditional vertical wheel will usually generate up and down events, while tilt wheels and trackpads may also produce horizontal deltas. Compare the latest label with the gesture you made, then repeat slowly and quickly. If an application behaves differently, test there too: this page proves only what reached this browser target during the session, not what every program or operating-system control will receive.

The cumulative X and Y values are signed sums. Opposite movements can cancel, so a total near zero does not mean that no scrolling occurred. The directional counts and total event count remain the better record of activity. A zero-delta event can be delivered by synthetic input or unusual browser handling and is preserved in its own bucket rather than silently discarded. Non-finite synthetic deltas are rejected, and counter overflow is guarded instead of producing misleading values.

This tool is not a mouse polling-rate checker, input-latency test, hardware diagnostic, repair guide, or accessibility assessment. Browser wheel events cannot reveal a USB polling frequency, physical encoder bounce, radio quality, driver health, or the exact moment a wheel moved. A missing direction can result from device capability, browser interception, gesture settings, remote desktop software, or the test method. Use manufacturer diagnostics or qualified support when hardware decisions depend on the result.

All event counts and deltas stay in the current tab. The widget does not upload gestures, save history, identify the device, request hardware permissions, or listen outside its test area. Refreshing, closing, or selecting Reset clears the session. The reliable contract is narrow: record finite browser wheel deltas delivered to the zone, apply a disclosed dominant-axis classification, keep transparent counts and signed sums, and avoid presenting those browser values as calibrated hardware measurements.

Methodology & sources

Accept finite WheelEvent deltaX and deltaY values only inside the visible test zone. Label a zero pair none. Otherwise compare absolute axes, use vertical for a tie, and derive up/down or left/right from the sign of the dominant delta. Immutably increment the total and chosen directional bucket, preserve the latest raw pair, and add signed cumulative X and Y values while rejecting non-finite totals and unsafe counter state. The UI prevents default scrolling only for events delivered to the zone. Tests assert all four directions, vertical ties, zero events, exact cumulative arithmetic, and invalid-delta rejection.

Frequently asked questions

Why do delta values differ between devices?
Browsers, operating systems, drivers, wheels, trackpads, acceleration, and event units can differ. The displayed values are raw browser event data, not normalized distance.
Does this measure mouse polling rate?
No. Browsers can combine or throttle wheel events, so event frequency and delta values cannot be treated as USB hardware polling rate.
Why can cumulative values return near zero?
They are signed sums. Movement in opposite directions can cancel even though directional and total event counts still show the activity.

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