PageSpeed Insights
What PageSpeed Insights Is
PageSpeed Insights is a free tool from Google that analyzes a single web page and reports how it performs for visitors. You enter a URL, and it returns results for mobile and desktop views.
The report combines two kinds of data. Field data comes from the Chrome User Experience Report (CrUX), which collects measurements from real Chrome users who visit the page. Lab data comes from a simulated test run by Lighthouse, the open source auditing tool, on Google's servers. Both sections appear on the same page, but they answer different questions. Field data shows what real visitors experience, while lab data shows how the page performs under one controlled setup. The difference is explained in the field data vs lab data article.
Field data is only available for pages or sites with enough recent Chrome traffic. For a small or new page, the field section may say that no data is available, and only the lab results will appear.
Reading the Opportunities and Diagnostics
The lab section lists the performance metrics it measured, such as First Contentful Paint and Largest Contentful Paint, along with the timing for each. Each metric has a short label that describes what it measures.
Two further groups of items help explain the results:
- Opportunities are suggested changes that might reduce load time, each with an estimated saving in seconds. The estimates are approximate and can overlap, so the savings should not be added together.
- Diagnostics are findings about how the page is built, such as the size of the document, the number of requests or long-running scripts. They do not always have a direct effect on load time.
Passed audits are listed separately, so a long list of checks does not always mean the page has many problems. The overall Lighthouse performance score at the top of the report is a weighted summary of the lab metrics only.
Reading a Report for a Local Business Site
A local bakery's website has a good field result for its largest visible element but a poor lab score on mobile. The opportunities list points to a large hero image and a chat widget that loads early. The owner can see that most visitors have a fine experience, while the lab test with a slower device shows a real cost for people on weaker phones.
Both sections are useful. The field data describes the current experience, and the lab items show where to investigate first. Neither section alone tells the full story.
Frequently asked questions
Is the PageSpeed Insights score the same as my real speed?
No. The 0 to 100 score comes from the lab test and is a weighted summary of simulated metrics. It can differ from what real visitors experience, which is shown in the field data section. Use the field section to understand real experience and the lab section to find the causes of slow results.
How often does PageSpeed Insights update its results?
Lab results are generated each time you run a test, so they reflect the page at that moment. Field data comes from CrUX, which aggregates visits over a rolling 28-day window. Because of that window, field results change gradually, and a fix may take several weeks to appear in that section.