What is Google PageSpeed Insights?
Google PageSpeed Insights is a free tool to help you find and fix issues slowing down your web application. An open-source tool called Lighthouse collects and analyzes lab data that’s combined with real-world data from the Chrome User Experience Report dataset. The result is a score that summarizes performance and a series of recommendations.
Diagram of How Lighthouse Works – Source: Google
The performance score is a weighted average of metric scores and the weight of each metric is a representation of the user’s perception of performance. You can experiment with the impact of different metrics on your score using the Lighthouse Scoring Calculator.
|First Contentful Paint (FCP)
||The first point in time when a user can see any page content on the screen.
|Speed Index (SI)
||The visual progression of a page load and how quickly the content is painted.
|Largest Contentful Paint (LCP)
||The time until the largest content element is fully visible on the screen.
|Time to Interactive (TTI)
||The amount of time it takes for a page to become fully interactive.
|Total Blocking Time (TBT)
||The severity of how non-interactive a page is until it becomes reliably interactive.
|Cumulative Layout Shift (CLS)
||How often a user experiences unexpected layout shifts.
Note: These weights are accurate for Lighthouse 6, but may change in future versions based on the Lighthouse team’s research on what has the biggest impact on user-perceived performance. In addition, your performance may vary each time you run the test due to the inherent variability in web and network technologies, even if the code hasn’t changed.
The aggregate performance score is divided into Good, Needs Improvement, or Poor categories based on the values of each weighted metric.
- Good: Scores of 90-100
- Needs Improvement: Scores of 50-89
- Poor: Scores of 1-49
Any score above 90 is considered good. In most cases, development efforts are better spent elsewhere once you’ve reached a good score – in fact, a 100/100 score is quite difficult to achieve on a consistent basis. The tool is best used for the recommendations, which the next section addresses in greater detail.
It’s Simple to Use
It’s essentially the same as Lighthouse. If you’d prefer, you can install Lighthouse as a Chrome plugin to avoid visiting Google PageSpeed Insights, and generate reports that you can save locally to reference.
That said, it’s easy to get started with Google PageSpeed Insights:
- Visit the Google PageSpeed Insights page
- Input your web page URL
- Click Analyze
After a few seconds of analysis time, you’ll see a report that shows the overall performance score along with a breakdown of different categories.
Example of Performance Results for Yahoo.com – Source: Google
The generated report is divided into several sections:
- Performance Score: The overall score
- Field Data: Google’s real-world data, if available
- Origin Summary: A review of the Core Web Vitals
- Lab Data: The metrics calculated from Lighthouse
- Opportunities: Suggestions to help the page load faster
- Diagnostics: More information about the performance of the application
You can toggle between the desktop and mobile versions of the report, which is helpful when optimizing the user experience. If you have a desktop-only web application, you may want to ignore the mobile performance report and focus exclusively on the desktop version.
The opportunities section is often the most helpful part of the report, as it provides tangible recommendations for improving performance.
Example of an Opportunity to Improve – Source: Google
In the example above, Google PageSpeed Insights indicates that the web application could benefit from next generation image formats, which could shave off nearly 20 seconds in loading time. The service even recognized the website as running on WordPress and suggested the use of a plugin that could automatically convert uploaded images into optimal formats.
There may be several items you need to optimize for your web application’s performance. We recommend focusing on the largest items first.
You Still Need Load Testing
Google PageSpeed Insights measures performance from a single user session and may include some aggregate data, but it shouldn’t be the only performance testing tool in your repertoire. For example, PageSpeed Insights doesn’t show you how a web application performs under an expected or unusually high load (e.g. a flash sale even for an ecommerce application).
LoadNinja makes it easy to add load tests to your performance test suite. While conventional load testing is an arduous process, LoadNinja’s Record and Replay functionality makes it easy to build load tests in a fraction of the time without sacrificing flexibility. You can then incorporate these load tests into your continuous integration (CI) processes to automate them.
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The Bottom Line: Test Smartly
Performance is critical to the success of any web application. Google PageSpeed Insights is a great tool to measure performance and receive relevant recommendations – but it shouldn’t be the only tool in your repertoire. LoadNinja and other tools can fill the gaps with load testing and other types of performance tests.