PageSpeed Insights (PSI) creates reports on the websites performance on both mobile and desktop devices, providing suggestions on how we can improve that website.
PSI provides both lab and field data about a website or page. Lab data is useful for debugging performance issues, as it is collected in a controlled environment. However, it may not capture real-world bottlenecks. Field data is useful for capturing true, real-world user experience - but has a more limited set of metrics. However it allow us to improve you photos, images, plugins, outsources, SSL Certificated, etc.
At the top of the report, PSI provides a rating that summarizes the page performance. This score is determined by running Lighthouse to collect and analyze laboratory data through the site. A score of 90 or more is considered good. 50 to 90 is a score. it needs improvement and under 50 is considered bad.
Real-World Field Data
When PSI is given a URL, it will look it up in the Chrome User Experience Report (CrUX) dataset. If available, PSI reports the First Contentful Paint (FCP), First Input Delay (FID), Largest Contentful Paint (LCP), and Cumulative Layout Shift (CLS) metric data for the origin and potentially the specific page URL.
Classifying Good, Needs Improvement, Poor
PSI also divides field data into 3 groups that describe experiences as good, in need of improvement or bad. The PSI sets the following threshold values for good / in need of improvement / bad, based on our analysis of the CrUX data set:
Distribution and Selected Metric Values
With PSI presents a distribution of these metrics we as your developers can understand the range of FCP, FID, LCP, and CLS values for your page or origin. This distribution is also split into three categories: Good, Needs Improvement, and Poor, denoted with green, orange, and red bars. For example, seeing 14% within FCP's orange bar indicates that 14% of all observed FCP values fall between 1000ms and 3000ms. This data represents an aggregate view of all page loads over the previous 28-day collection period.
Above the distribution bars, PSI reports the 75th percentile for all metrics. The 75th percentile is selected so we can understand the most frustrating user experiences on your site. These field metric values are classified as good/needs improvement/poor by applying the same thresholds shown above.
Core Web Vitals
Core Web Vitals are a common set of signals critical to all web experiences. The Core Web Vitals metrics are FID, LCP, and CLS, with their respective thresholds. A page passes the Core Web Vitals assessment if the 75th percentiles of all three metrics are Good. Otherwise, the page does not pass the assessment.
Differences Between Field Data in PSI and CrUX
The difference between the field data in PSI and the Chrome User Experience Report in BigQuery is that the PSI data is updated daily for the past 28 days. The dataset in BigQuery is only updated monthly.
We apply PSI uses Lighthouse to analyze the given URL, generating a performance score that estimates the page's performance on different metrics, including: First Contentful Paint, Largest Contentful Paint, Speed Index, Cumulative Layout Shift, Time to Interactive, and Total Blocking Time.
Our audits separates its into three sections:
Opportunities provide suggestions how to improve the page’s performance metrics. Each suggestion in this section estimates how much faster the page will load if the improvement is implemented.
Diagnostics provide additional information about how a page adheres to best practices for web development. Passed Audits indicates the audits that have been passed by the page.
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