Test your hardware before you blame it
Most hardware faults are easy to confirm and hard to describe. A key that only fails when you hold Shift, a mouse that double-clicks one time in twenty, a monitor that quietly runs at 60 Hz instead of the 144 Hz you paid for — these are the problems these testers are built to catch. Each one reads the raw events your browser receives from the device, so what you see is what your operating system is actually sending, not a guess.
Start with the keyboard tester if keys are sticking, ghosting or not registering: it lights up every key on a real layout and flags chatter and missed presses. The mouse tester checks each button, the scroll wheel and the double-click fault that worn switches develop. For displays, the dead pixel test fills the screen with solid colours so stuck and dead pixels stand out, and the refresh rate test measures the Hz your screen is really running at.
There are also testers for webcams, microphones, speakers, gamepads and touch screens. Camera and microphone checks ask for permission first, and the audio and video never leave your device — nothing is recorded to a server, and there is nothing to install or sign up for. If a result looks wrong, each tool page explains what it measures, what a healthy result looks like and what to try next.