Scroll Wheel Tester

Scroll inside the test zone on this page. If the direction indicator (⬆️/⬇️) updates and the event counter increments, your scroll wheel is sending correct signals to the browser. A healthy scroll wheel should register one event per notch click. If nothing happens when you scroll, try a different browser or check your mouse driver settings.

Smooth scrolling produces fractional delta values (e.g., deltaY = 4.666) rather than fixed integer steps (e.g., deltaY = 120). Trackpads (Apple Magic Trackpad, laptop touchpads) and premium mice with free-spinning wheels (Logitech MX Master) typically produce fractional deltas. Standard notched scroll wheels produce integer deltas. This tester shows '✨ Smooth scroll' when fractional deltas are detected.

The delta value (deltaY or deltaX) is the distance unit reported by the browser per scroll event. A standard mechanical scroll wheel typically sends deltaY = 100 or 120 per notch in most browsers. Smooth-scrolling devices send smaller fractional values per event. The deltaMode property (0 = pixels, 1 = lines, 2 = pages) affects interpretation, but most browsers normalise to pixel mode.

Scroll behavior is controlled at multiple levels: hardware driver, OS, and application. Some applications intercept scroll events before the browser sees them, or use custom scroll handlers that ignore OS-level smooth scrolling settings. If your scroll works here but not in a specific app, the issue is application-level, not hardware. If it fails everywhere, check your mouse driver (Logitech Options, Razer Synapse, etc.) for scroll direction or speed overrides.

Events per second (eps) measures how many scroll wheel events your mouse sends in one second. A standard scroll wheel typically fires 3–8 events per second at moderate speed. Enthusiastic scrolling can reach 15–25 eps. High-end mice with free-spinning momentum wheels or fast trackpad flicks can exceed 40 eps. The 5-second timed test measures your average eps across the full duration.

Scroll jumping — where the page moves too far per notch — is usually caused by OS scroll speed settings, not hardware. On Windows: Settings → Bluetooth & devices → Mouse → Scroll → adjust 'Lines to scroll at a time'. On Mac: System Settings → Mouse → Scrolling Speed. If the hardware scroll wheel encoder is failing, you may see erratic deltaY values (e.g., mixing +120 and -120 in the same direction), which this tester will show in the delta readout.

On Windows 11/10: open Settings → Bluetooth & devices → Mouse → Additional mouse settings → Wheel tab — there is no native reverse option, so use PowerToys Mouse Utility or your mouse manufacturer's software (Logitech Options, Razer Synapse). On Mac: System Settings → Mouse → toggle 'Natural scrolling' off to reverse direction. On Linux: add 'Option "ZAxisMapping" "5 4 7 6"' to your Xorg mouse config. Note that reversing trackpad direction on Mac also reverses the external mouse unless you use an app like Scroll Reverser.

Yes — dust is one of the most common causes of scroll wheel failure. Mechanical scroll wheels use an optical or mechanical rotary encoder that can be fouled by dust, hair, or skin debris. Symptoms include inconsistent delta readings, missed ticks, and erratic direction changes. To clean: power off your mouse, use a can of compressed air aimed at the scroll wheel gap, and gently rotate the wheel while blowing. For severe buildup, disassemble the mouse and clean the encoder wheel with isopropyl alcohol (90%+). After cleaning, rerun this tester — consistent integer deltas per notch confirm the encoder is healthy.

Ghost scrolling (also called phantom scrolling) is when your page scrolls on its own without you touching the wheel. It is almost always caused by a dirty or failing rotary encoder sending phantom pulses to the browser. To diagnose it: open this tester, place your hand away from the mouse, and watch the event counter — if it ticks on its own, your encoder is producing ghost events. Fixes to try in order: (1) Clean the scroll wheel with compressed air. (2) Update or reinstall your mouse driver. (3) If you use a wireless mouse, replace the battery — low voltage causes erratic sensor behavior. (4) If problems persist, the encoder needs replacement or the mouse needs to be retired.

Yes, in most cases. A failing mechanical encoder produces characteristic signatures this tester can reveal: random deltaY sign flips while scrolling in one direction (the delta readout shows +120 followed by -120 without you changing direction), inconsistent delta magnitudes per notch, or ghost events that fire with the wheel stationary. Run the tester for 30 seconds of deliberate scrolling — if you see direction reversals you did not make, or the event counter increments on its own, the encoder is the likely culprit. Note that some encoder failures are intermittent and only appear when the mouse is warm or under load; repeat the test if symptoms are inconsistent.

No — mobile and tablet devices do not have a physical scroll wheel, so there is nothing to test. Touch-based scrolling (finger swipe + inertia) uses a completely different event system (TouchEvent / PointerEvent) rather than the WheelEvent API this tester listens to. If you open this page on a phone, you will see the interface but no scroll events will register. For testing a Bluetooth mouse connected to a tablet, the WheelEvent API may or may not fire depending on the browser and OS — results are unreliable. Use a desktop or laptop with a physical mouse for accurate scroll wheel diagnosis.