Lab measurement of one page load
What this check looks for
These are the timings and the resource breakdown from a single controlled load of ‹scope› in a browser we drive. They show where the time and the bytes go.
Why it matters
Field data tells you that the site is slow; a lab run tells you which resource is responsible. Use this to find the cause and the field section to confirm the cure.
What it costs your score
This check never deducts. It reports a fact — or reports that something could not be verified — and is shown on the report without moving the score.
- Severity
- info
- Default confidence
- confirmed
- Status when triggered
- info
- Deduction
- 0 points
- Family cap
- none
- Category
- Performance
- Module
- Perf lab
- Fix owned by
- user
- In the ruleset since
- 2026.09
Technical detail
‹detail›
This came from **one page load we performed**, not from your visitors. A lab measurement is reproducible and tells you exactly which bytes and which resources are responsible — which is why the numbers below are byte counts and resource lists rather than a score. What real visitors experience is in the field-data section, which is the evidence this report scores Core Web Vitals on.
**Metric timings are indicative, not authoritative.** ‹score note› They come from one throttled load — the connection shaped to a slow-4G profile and the CPU slowed by a fixed multiplier — and they vary run to run. Where they disagree with the field data, the field data wins: it is a distribution over thousands of real visits and this is a single sample.
The resource breakdown beside them does not have that weakness. Transfer sizes, request counts and per-type totals are facts about what your server sent, identical on any machine, and they are what the opportunity findings in this section are computed from.
Standards and references
Test this on your domain
Run the check that produces this finding, on its own, against any domain.
Other perf lab checks
- The page ships more JavaScript than it uses
- Images are served in older, heavier formats
- Images are much larger than the space they are shown in
- Stylesheets and scripts stop the page from rendering
- This report never publishes a headline performance score
- Static files are re-downloaded because they are barely cached
- Scripts and stylesheets are sent without compression
- The page was not measured in a browser