How to use this test
- Read the detected list. Everything in the first table comes from a real browser API. Where a value is approximate or derived, the note says so.
- Read the undetectable list. The second table is the point of this page. Those values have no web API at all.
- Copy the report. Useful for support tickets and forum posts — it captures what your browser actually reports.
- Run a benchmark for the rest. You cannot read what your CPU is doing, but you can measure what it can do.
What a browser can actually see about your PC
Every value in the first table above is read from a real browser API. Every value in the second table has no API at all — not a restricted one, not a permission-gated one. It simply does not exist.
That distinction matters because a whole category of sites blurs it, and people make purchasing and repair decisions based on numbers those sites invented.
Why the sandbox exists
A web page is untrusted code from a stranger. It runs inside a sandbox that can see its own tab and almost nothing else, and that boundary is what makes it safe to click a link.
If pages could read CPU load, memory usage and running processes, then any site you visited could profile your machine, work out what software you run, and identify you across the web with considerable accuracy. Hardware characteristics are unusually good fingerprints because they change rarely and are hard to fake.
That is why even the values browsers do expose are deliberately degraded — memory rounded into buckets, GPU strings masked, timers made deliberately imprecise. The trend is toward less information over time, not more.
The fabrication problem
Visitors arrive expecting Task Manager in a browser, and some sites give them something that looks like it. We examined a popular competitor’s "CPU Temperature Monitor", which displays a red LIVE indicator and claims real-time monitoring updating every second. The code behind it:
| Displayed as | Actually computed as |
|---|---|
| CPU temperature | 45 + random() * 15 |
| GPU temperature | 50 + random() * 20 |
| CPU fan speed | 1800 + random() * 400 |
A slow sine wave is added on top so the numbers drift convincingly. It is not a bug or an approximation — it is a random number generator with a thermometer icon.
This is worth caring about beyond principle. Someone worried their laptop is overheating may see a comfortable 52 °C and stop investigating a real thermal fault. A fabricated reassurance is worse than no reading at all.
What to do instead: measure, do not read
The useful reframing is that you cannot read machine state, but you can measure machine capability. Running real work and timing it is entirely possible, and it answers a better question anyway.
| You wanted to know | Impossible reading | Real measurement |
|---|---|---|
| Is my CPU slow? | CPU usage % | CPU benchmark — timed integer, float and memory work |
| Is my GPU struggling? | GPU load and temperature | GPU benchmark — sustained frame rate, with throttle detection |
| Is my RAM slow? | RAM usage | Memory test — real bandwidth and latency |
| Is my connection bad? | Router statistics | Speed test — real throughput, latency and jitter |
| Is my screen right? | Panel specifications | Monitor test — measured refresh rate |
A benchmark answers "how capable is this machine" rather than "what is it doing right now", and for almost every real question — should I upgrade, is something wrong, did that change help — the benchmark is the more useful of the two.
Notes on the values we do show
- Logical cores counts threads, not physical cores. A six-core chip with hyper-threading reports twelve.
- Refresh rate is measured from presented frames, not read from the display. Laptops routinely drop to 60 Hz on battery without announcing it.
- Device pixel ratio is your OS scaling. A value of 1.5 means 150% scaling, which is why a 2560-wide screen may report 1707 logical pixels.
- Connection type is a browser hint, not a measurement. It is frequently wrong. Use the speed test.
- Storage quota is this site’s allowance, derived from free space but capped far below it.
Related tools
Start with the CPU benchmark if you want to know how your machine actually performs, or the monitor test to confirm your display is running at the refresh rate you paid for.
Frequently asked questions
Why can a website not see my CPU usage or RAM?
Because no API exists for it, deliberately. Web pages run in a sandbox that cannot inspect anything outside their own tab — that is what stops a random site profiling your machine, enumerating your software, or fingerprinting you across the web. The restriction is a security feature, not an oversight, and it will not be lifted.
Other sites show my CPU temperature. How?
They make it up. We checked one popular competitor and its "live" temperature monitor is literally 45 plus a random number, with a sine wave added so the graph looks plausible. There is no thermal sensor API in any browser, so any live temperature you see on a web page is generated rather than measured.
What about performance.memory? That shows memory usage.
It shows this browser tab’s JavaScript heap — typically a few megabytes — and it only exists in Chromium browsers. It has no relationship to your system memory usage. Sites that present it as RAM usage are misreading the API.
Why does my memory show as 8 GB when I have 32?
navigator.deviceMemory is deliberately bucketed to 0.25, 0.5, 1, 2, 4 or 8 and capped, because exact memory size is a strong fingerprinting signal. It reports installed memory, never usage, and the cap is intentional. Treat it as a rough class rather than a specification.
Why is my GPU shown as "Masked by browser"?
The WebGL renderer string is being withheld. Firefox restricts it by default, private and hardened modes hide it, and Chromium is progressively reducing its detail. It is one of the strongest fingerprinting signals available to a web page, so browsers are steadily closing it off.
Is my storage quota the same as my free disk space?
No, and this trips people up constantly. It is how much this individual site is permitted to store, calculated from available space but capped well below it. It tells you nothing reliable about your drive size, and it changes as your disk fills.
Can a website see my MAC address or serial number?
No. Permanent hardware identifiers are blocked outright in every browser, because they would allow tracking that no privacy setting could defeat. Any site claiming to show yours is fabricating it.