What this test does
A CPU stress test keeps the processor busy at full speed so you can check that it stays stable, see how hot and loud the machine gets, and find out whether performance drops as it warms up. This page starts one Web Worker per thread you choose. A worker is a background thread provided by the browser, and each one runs a tight loop of floating-point square roots and integer arithmetic, counting how many operations it completes. The page shows the speed of every thread and the total, updated twice a second.
Reading the results
Operations per second are a relative score, useful for comparing runs on the same device: before and after cleaning a fan, on battery and plugged in, or with one thread versus all of them. Running one thread shows single-core speed. Running as many threads as logical processors shows multi-core throughput; the total should rise almost linearly until you reach the number of physical cores, then more slowly because hyper-threads share hardware. At the end the tool compares the last seconds with the first. A drop of more than about 10–15% usually means the processor reduced its clock speed to manage heat (thermal throttling) or power.
Limits of a browser test
Browsers may limit background tabs, so keep the page visible. A browser cannot read temperatures, clock speeds or fan speeds; use your operating system's monitoring tool, or a utility such as HWiNFO, alongside the test if you need them. Native benchmark programs push the CPU harder with vector instructions, so a browser stress test is gentler and safer, but it is still a real full load.
Safety
Modern processors protect themselves by slowing down or shutting off before damage occurs, so a short test is safe on a healthy machine. Still, stop the test if the device becomes uncomfortably hot, if it is a phone in a case, or if the cooling is blocked. The test always ends on its own when the duration runs out, and closing the tab stops every worker immediately.