CPU Stress Test
Run a JavaScript load on the threads you pick, chart throughput, and compare one thread with many. Nothing to install.
Ready.
This tries to keep every selected worker busy. Laptops can get hot, fans can spin up, and the battery drains fast. Stop any time. The test pauses when you switch tabs, because browsers slow background pages, and that pause is not scored. Points stand for 100,000 loops per second, so only compare scores from this page in the same browser.
What a browser CPU stress test tells you
What it can and can't do
The page starts one Web Worker per selected thread. Each runs a tight loop of square roots, sines and multiply-adds, and reports how many loops it finished. That measures throughput. It is still JavaScript in a sandbox: no AVX vector loads, no memory torture, no error checking. Prime95, OCCT or Cinebench pull far more power, so a pass here does not prove an overclock is stable.
Logical threads and hardwareConcurrency
The thread count comes from navigator.hardwareConcurrency, which reports logical threads, not a physical processor count. A chip with 8 processors and hyper-threading shows 16. Some browsers cap or fake the number for privacy: Firefox with fingerprinting protection reports 2, and Safari has been known to report no more than 8. The multi-thread score should rise when more workers stay busy.
Reading the throttling curve
The page cannot read temperature or watts. A falling line only means throughput dropped. A flat line is the usual desktop pattern. Many laptops boost, then settle lower within a minute. The page cannot name the cause. Run it plugged in, then compare with the run on battery. A hidden tab is not counted.
Checking a used laptop or a listing
Buying second-hand? Run the 5 minute test in the seller's browser. A line that falls hard means throughput dropped. It does not by itself prove the cooling needs work. If the listing says 16 threads, the reported thread count should say so, and the multi-thread score should be well above the single score. A scaling factor near 1x on a "16-thread" machine is a red flag.
Safety
Modern CPUs protect themselves by slowing down before they overheat, so a browser test will not damage working hardware. Keep vents clear, do not run long tests on a laptop on a bed or lap, and stop if the machine shuts off: that is a cooling or power fault worth fixing.
Related tools
Load the graphics card with the GPU stress test, check smoothness with the FPS test, and work out real memory latency from CL and speed with the RAM latency calculator.
Frequently asked questions
Does this read temperature or watts?
No. The browser cannot see package temperature, power draw, or fan speed. The chart is only how many loops this page finishes per second. A falling line means throughput dropped. It is not a thermometer and it is not a watt meter.
What does the thread count mean?
The figure is navigator.hardwareConcurrency when the browser provides it. That is a hint of logical threads, not a physical processor count, and it can be missing or capped. Some privacy settings report 2. When it is missing, the page shows a question mark and does not invent a number. You pick how many workers to run.
Why do I see a dash instead of 0?
A score needs finite samples. An empty run, a divide by zero, or a rate that is not a finite number shows a dash. The page does not show 0, NaN, or Infinity as if that were a result. A stress run shorter than 5 seconds is not saved.
Why did it pause when I left the tab?
Browsers slow timers and workers in a hidden tab. That slowdown is not a weak CPU, and the page does not record it as a failed run. Workers stop while the tab is hidden and start again when you come back. Keep this tab visible for a real reading.
Is the points score a Cinebench result?
No. One point stands for 100,000 JavaScript loops per second on this page. It is not Cinebench, Geekbench, or any other named benchmark. Compare points only with other runs from this page in the same browser.
Can this damage the computer?
The work is JavaScript in the browser. A laptop can get hot, fans can get loud, and the battery can drain fast. Chips slow themselves before they overheat. Stop any time. If the machine powers off, that is a cooling or power fault. Passing here does not prove an overclock is stable.
Does the load start when the page opens?
No. Nothing runs until you press Start stress test or Benchmark. Stop ends the workers and the timer. Leaving the page does the same, so the CPU is not left busy in the background.