Finding a faulty mouse button
The most common mouse fault is a worn switch that “chatters”: you press the button once, but the computer receives two clicks, so files open when you meant to select them and drag-and-drop lets go by itself. A human cannot click twice within about 80 milliseconds on purpose, so this tester flags any two presses of the same button closer than the threshold you choose. Click slowly and deliberately, one press at a time; if the suspicious counter keeps rising, the switch is probably failing. Some gaming mouse software includes a “debounce” setting that can hide the problem for a while.
All five buttons and the wheel
The pad counts left, right and middle (wheel) clicks plus the two side buttons used for back and forward, and lights up the matching part of the mouse picture while a button is held. Right-click menus and middle-click actions are disabled inside the pad so you can test freely. The wheel counter goes up as you scroll down and down as you scroll up; if it jumps in the wrong direction while you scroll steadily, the wheel encoder may be dirty or worn. Touchpads and touch screens produce similar events, though a touchpad's two-finger scroll sends many small steps.
Polling rate
A mouse reports its position to the computer many times per second: 125 Hz for basic office mice, 500 or 1000 Hz for gaming mice, and up to 4000–8000 Hz for some newer models. The tester collects pointer movement events, including the extra “coalesced” events modern browsers provide, and takes the median time between them. Move the mouse quickly in circles to get a stable estimate. Browsers and operating systems can limit how many events reach a web page, so very high rates may read lower than the true value, but the test easily shows whether a mouse is running at 125, 500 or 1000 Hz.
Privacy
All counting happens in the page. Nothing about your clicks or movement is recorded or sent.