Google offers free tools to identify and prioritize web performance issues, which is the first step towards improving web performance. Two approaches to analyzing web performance are lab tests and field data. Lab tests involve emulating a device and are useful for discovering specific performance issues, whereas field data takes into account real user experiences. Google’s Lighthouse is an open-source program that offers synthetic testing, and the Chrome UX Report collects field data from users. Users can access these tools in several ways, including automated audits through PageSpeed Insights, Lighthouse analysis through the Developer Tools tab in the Chrome browser, and exploring raw data through the command line interface of BigQuery.

PageSpeed Insights provides an easy-to-interpret report on page load speed and opportunities for improvement. The tool is accessible via a simple web interface, and users can simply insert the URL of interest and press the Analyze button. The audit for the mobile experience is displayed by default, and the audit for the desktop experience is available in a separate tab. The first report shows the page’s Core Web Vitals, measured for real users navigating with Chrome Browser over the last 28 days. The metrics are given for the 75th percentile. Users can observe if their page fails the Core Web Vitals assessment, which can be bad for conversions and SEO.

The next part of the audit involves lab testing, which reproduces the loading experience in a controlled environment. This helps to identify the sources of poor performance. The audit is powered by Google Lighthouse, which emulates a connection on a Moto G4 mobile with a slow 4G connection. The page is rated for four aspects: loading performance, accessibility, UX best practices, and SEO optimization. The scores are normalized, with a score below 50 considered poor and marked in red.

While Google Lighthouse is a reference for lab testing, it lacks flexibility when used out of the box. An alternative with more flexibility is provided by WebPageTest, which can emulate a much wider range of conditions.