Load your graphics card straight from the browser and watch what it does: the frame rate against your screen's refresh rate, and the artifacts, flicker and driver resets that a failing GPU shows under load. Nothing to install.
The stress scene appears here once you start.
This page loads your graphics chip and shows you what happens. Here is how to read the result — and where the honest limits of a browser are.
Your screen decides how many pictures a second you can possibly see. On a 60 Hz screen a healthy graphics card sits at exactly 60 and stays there however hard you push it, because it is waiting for the screen rather than struggling. That is why the chart draws your refresh rate as a line: the useful reading is not the number, it is the level at which the line finally falls away from it.
No script can see corrupted pixels the way you can. Artifact watch holds a steady load and mixes in high-contrast patterns, because snow, blocks, wrong colors and flashes stand out against them. Watch the picture rather than the numbers for a minute or two, and take a photo if you see something — it is the evidence a repair shop will ask for.
If the graphics driver crashes and restarts mid-run, the browser tells the page that it has lost its device. This test catches that and says so, instead of leaving a blank rectangle behind. A driver reset under load is one of the strongest signals there is that something is genuinely wrong — with the drivers, an overclock, the cooling, or the memory on the card.
Hold one fixed level for several minutes and watch the line. A frame rate that stays flat is a chip living within its thermal limits. One that starts high and slides down while nothing else changed is throttling: the chip slowing itself to stay cool. Dust, dried thermal paste and blocked vents are the usual causes.
Laptops carry two graphics chips: a low-power one inside the processor and, sometimes, a faster separate card. The browser asks for the fast one, but the operating system has the final say, and on battery it often says no. The renderer name at the top of this page tells you which one actually answered — that alone explains a lot of surprisingly low results.
Update your graphics drivers, check that hardware acceleration is switched on in your browser's settings, plug the laptop in and take it off any battery-saving profile, close other tabs and apps that use the GPU, and on Windows point your browser at the high-performance GPU under Settings → System → Display → Graphics.