Calibrate the action, then inspect the pattern
Natural scrolling and software remapping can change how movement relates to delta signs. This tool labels direction from the action you choose in the current run instead of relying on a platform-wide guess.
How to use the Scroll Direction Test
Select Up or Down
Treat each direction as a separate scroll direction test and reset before switching stages.
Provide calibration events
Make at least three clear movements in the selected direction without intentionally reversing.
Continue steadily
Review expected events, opposite candidates, and longest same-direction sequence, then repeat the stage.
Why a scroll direction test needs calibration
A `WheelEvent` exposes numeric deltas, but the sign should not be interpreted without context. Natural-scrolling preferences can change the relationship between a hand movement, content motion, and the delta reported to an application. Drivers or accessibility tools can remap input as well. The scroll direction test therefore asks what you intend to do, samples the dominant sign, and calls that sign the baseline for this run.
After calibration, the mouse scroll direction counts matching events as expected and opposite signs as candidates. The visual arrow represents your selected action; it does not claim that positive always means Down on every system. Recalibration is important after changing direction, device mode, browser, operating-system setting, or software profile.
Separate intentional reversals from unexpected ticks
An intentional switch from Up to Down should create the opposite sign. That is ordinary behavior, not a fault. During a one-direction run, however, an isolated opposite event surrounded by baseline events may be worth repeating. A short cluster can reflect a real reversal, inertia, gesture correction, remapping, or another factor. This reverse scroll test calls it a candidate because the event stream does not contain the cause.
Frequent alternating signs make calibration unstable and are shown as mixed input. That result commonly appears when a user rocks the wheel, changes direction, or uses a touchpad gesture with momentum. Repeat with slower, separated strokes. If mixed input remains while your physical motion is clearly one-way, proceed to the jitter test for stroke-level context rather than concluding that hardware is damaged.
Mouse, touchpad, and trackball behavior
A mouse wheel may create compact step-like bursts. A touchpad may produce many small events and an inertial tail, while a trackball or accessibility device can use its own mapping. All may trigger the same browser `wheel` event. The scroll direction test cannot reliably name which device produced the input, so it compares signs within the run and avoids device-specific diagnosis.
For a touchpad, lift your fingers cleanly and wait for momentum to stop before changing stages. For a free-spin wheel, stop the wheel before the Down run follows the Up run. A controlled notched wheel can be tested in short groups of steps. Consistent technique reduces false reverse candidates and makes repeated up and down scroll tests easier to compare.
Natural scrolling and system settings
If page movement is consistently opposite to your preference across every application, check the system’s natural-scrolling or direction option before examining hardware. If only one application behaves differently, inspect that application or a vendor profile. The browser’s raw sign is less important than whether your selected action produces a stable baseline and the content moves as configured.
After changing a setting, reset the scroll direction test because the previous baseline no longer describes the environment. Test both stages again. If the browser reports consistent events but the page does not move, remember that `wheel` and `scroll` are different events: an application may cancel, transform, or use wheel input without moving a document.
When to inspect software and when to inspect hardware
Start with software when the direction is consistently reversed, differs by application, or changes with a profile. Check system settings, official vendor software, browser extensions, and accessibility features. Test another browser and another device where practical. A setting-related pattern often changes when one of those layers changes, while the mouse scroll direction remains internally consistent.
Consider a physical or connection factor only after repeatable controlled runs show unexpected candidates across applications and settings. For wireless devices, review charge, receiver placement, and connection mode. Clean only external surfaces after disconnecting power and follow manufacturer instructions. Do not open equipment under warranty based on a web result; use qualified support when disassembly would be required.
Scroll Direction Test questions
Does positive deltaY always mean scrolling down?
No universal hardware conclusion should be based on sign alone. This page calibrates the sign from the action you choose in the current environment.
Why did the Up run show mixed input?
You may have reversed, momentum may have continued, or the first calibration events may not have been stable. Stop motion, reset, and repeat more deliberately.
Can natural scrolling make the mouse faulty?
No. Natural scrolling is a direction preference. Change it in system settings if page motion is consistently opposite to what you want.
What should I do with one opposite event?
Repeat the same controlled stage several times and use the jitter test. One browser event is not enough to identify a cause.