CPU stress test online. Every core, held under load.
Load every core of your processor from this browser and see whether it keeps its speed. Nothing to install, no account, 3 minutes for the whole run.
Illustrative run. Your own cores draw their own.
Load
Every logical core
CPU stage
60 s, longer on Deep
Sampling
Every 250 ms
Reports
Slowdown, steadiness
Full load, measured for a full minute.
The CPU stage is the first part of the free run. It holds every core at work long enough for a power or heat limit to show itself.
- Every logical core
- Web Workers run the same work on every logical core the browser reports, so the whole processor is loaded, not one thread.
- Speed every quarter second
- Throughput is recorded in 250 ms windows, so the result is what the processor delivered across the minute rather than one peak moment.
- Past the short power budget
- Many laptops allow extra power for the first 28 seconds or so. A 60 second stage runs past that point, so a machine that drops when the budget ends shows it.
- A deeper run for heat
- The free Deep run takes 9 minutes, holds the CPU for two and a half minutes to reach thermal saturation, and re-tests it hot.
What the numbers tell you about your processor.
A stress test is only useful if it says what happened over time. These are the CPU figures the report shows for free.
Slowdown
How much speed the processor lost after its boost ended and it settled. A short boost and one step down early in the stage are normal and shown on their own as the boost step. A drop smaller than the run's own noise is shown as within noise rather than as a loss.
Steadiness
How evenly the work was delivered, out of 100. Low steadiness usually means something else on the machine was competing for the processor.
The shape of the curve
Whether the speed held, stepped down once when a power budget expired, or slid steadily as the cooling fell behind. Each points at a different cause.
Speed as a floor
A browser cannot reach the absolute peak of a native tool, so read the absolute number as a floor and the change over time as the real result.
Illustrative run. Your own cores draw their own.
Hardware
What it needs. Three tiers, no fine print.
Minimum
Any recent browser
Chrome, Edge, Firefox or Safari on a laptop or desktop completes the stage.
Recommended
Plugged in, other apps closed
Background work and battery saving both change the result, so close heavy apps first.
Optimal
The Deep run
9 minutes, with a hot re-test, for a machine you suspect of overheating.
In short
CPU stress test: the answer first
A CPU stress test online loads every logical core from Web Workers and records the work done every quarter second for a full minute, longer on the Deep run. If the processor keeps its speed, the line stays flat; if it gives some up when a power budget ends or as heat builds, the curve shows when and by how much.
Reading your result
- One early step is normal
- Many processors boost for a short budget and then settle. The report shows that boost step on its own, so a single early drop is not counted against the machine.
- A steady slide is worth a look
- Speed that keeps falling through the stage is consistent with cooling falling behind, alongside look-alikes such as a background task. A sensor tool confirms which one it is.
- Low steadiness points elsewhere
- When the work arrives unevenly, something else on the machine was usually competing for the processor. Close it and run again before reading the slowdown.
What good looks like
The ranges, before you run it.
Slowdown under long work
- Under 8%
- Holds its speed
- Little lost over the run.
- 8% to 15%
- Normal
- Common on laptops and compact PCs.
- 15% to 30%
- Noticeable
- Long tasks run clearly slower than short ones.
- 30% or more
- Worth checking
- Often heat, dust or a low power limit.
Processor steadiness
- 90 or more
- Steady
- Work is delivered evenly.
- 75 to 89
- Some unevenness
- Small dips, often background apps.
- Below 75
- Uneven
- Something else may be competing for the processor.
Overall score (provisional bands)
- 85 to 100
- Excellent (provisional)
- Fast, and it keeps its speed under long work.
- 70 to 84
- Strong (provisional)
- Comfortable for demanding work.
- 55 to 69
- Good (provisional)
- Fine for everyday and moderate work.
- 40 to 54
- Modest (provisional)
- Everyday tasks; heavy work will feel slow.
- Below 40
- Limited (provisional)
- Struggles with sustained work.
What a browser cannot see
The honest limits, and where to look instead.
- How full your memory isA web page cannot see how much memory is in use. If the machine slows down with many apps or tabs open, check it directly.
- On a MacActivity Monitor, Memory tab: Memory Pressure at the bottom. Yellow or red means memory is the limit.On WindowsTask Manager (Ctrl+Shift+Esc), Performance, Memory. Above about 85% in use while you work means memory is the limit.
- Temperatures and fan speedNo browser can read a temperature sensor, so heat shows here only as speed lost over time.
- On a MacA free app such as Stats shows temperatures and fan speed.On WindowsHWiNFO, or your laptop maker's own app.
- Storage speed and healthOpening apps and files depends on the drive, which this test does not touch.
- On a MacDisk Utility, then First Aid on your main drive.On WindowsCrystalDiskInfo shows the drive's health status.
Questions
CPU stress test, answered
- Is an online CPU stress test safe?
- Yes. A modern processor slows itself down long before heat can damage it, and that slowdown is what this test measures. Close the tab and the load stops at once.
- How long should a CPU stress test run?
- The CPU stage runs 60 seconds inside a 3 minute run, which is enough to show a power limit. For heat problems use the Deep run, which holds the load for two and a half minutes and re-tests the processor hot.
- Can a browser really load every core?
- Yes. Web Workers let a page run work on every logical core at once, which is enough to show a power or heat limit. It will not reach the absolute peak of a native benchmark, so compare the curve rather than the raw number.
- Does it show my CPU temperature?
- No. No browser can read temperature sensors. The test measures lost speed instead, and the report says what the shape of that loss most likely means.
- Do I need to download anything?
- No. The test runs in this browser tab. There is no install and no account, and every measured number in the report is free.
- How is this different from Prime95 or Cinebench?
- Those are native programs that reach a higher absolute load. This runs in the browser with nothing to install and records the whole curve, so it answers whether the processor holds its speed rather than how high it peaks.