What screen tools are on this site?
Eleven: four screensavers, five prank screens and two display tests, all running in the browser with nothing to install.
They share the same shell as the colour screens, so brightness, the wake lock and the timer work the same way on every one.
Which tool checks a monitor for faults?
Two do. The dead pixel test finds individual failed pixels; the uniformity test finds backlight bleed, clouding and colour tint across the panel.
Run the dead pixel test first, since it takes seconds and a faulty pixel is the more common complaint — and if you find one, stuck versus dead decides whether it is worth trying to fix. The uniformity test needs the room lights off to be worth anything, because ambient light masks exactly the differences you are looking for.
Which screensaver is best to leave running?
The DVD screensaver on a spare display, or the flip clock if you want the time. Both keep moving, so neither risks burn-in.
The DVD screensaver hits a corner every 35 seconds here and keeps a count. Matrix rain looks better but redraws every frame, so it costs more battery on a laptop.
Are the prank screens safe to use?
Yes. They are ordinary web pages that draw a picture of a crash or an update. Nothing is installed and nothing is changed.
Every one exits with Escape and none can block input outside the browser. The fake Windows update page explains the difference between a prank like this and real scareware, which is worth knowing either way.