GTmetrix Performance Blog

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Everything you need to know about the new GTmetrix Report (powered by Lighthouse)

We’re excited to present a detailed look at the new GTmetrix Report – powered by Lighthouse!


 

Overview

GTmetrix has undergone its biggest change yet, replacing the PageSpeed/YSlow libraries with Lighthouse, the industry standard in web performance.

With GTmetrix now being powered by Lighthouse, the new GTmetrix Report has been redesigned extensively to incorporate the Lighthouse data and metrics.

A new scoring system has been implemented, creating an all-new GTmetrix Grade, alongside new Performance and Structure Scores. The new GTmetrix Report also sees the addition of new tabs, visualizations, graphs, and deeper insights.

In this article, we’ll explain in detail all the changes to the new GTmetrix Report, as well as, how it compares to the old PageSpeed/YSlow reports, hereafter dubbed Legacy Reports.

 


 

Grading and Scoring Details

The scoring system used in the new GTmetrix Report is loosely based on the Lighthouse scoring system. However, it has been augmented by our own expertise and proprietary formulas to deliver the unique GTmetrix flavour that users have come to love and trust over the years.
 

The new GTmetrix Grade and Performance/Structure Scores

 
The resultant product is the new GTmetrix Grade – a weighted grade derived from the new Performance and Structure Scores, which replace the old PageSpeed and YSlow Scores (Legacy Reports).

 


 

GTmetrix Grade

The GTmetrix Grade blends how fast your page performs (in terms of loading, interactivity, and visual stability) with how well it’s built for optimal performance.

This grade better reflects your overall webpage experience as it accounts for, both, your front-end structure, as well as, the actual performance experienced by the user.
 

The GTmetrix Grade is an aggregate representation of your visitors’ page load experience, both, how well it’s built and actual performance.

 
The GTmetrix Grade is a weighted average of the two new percentage-based scores, namely:

  • The Performance Score (70%)
  • The Structure Score (30%)

The GTmetrix Grade is based on a simple formula, which currently assigns a 70/30 weighting for the Performance and Structure Scores respectively.

Note that this is our initial take on the GTmetrix Grade and Performance & Structure Scores, which are continually being monitored and tweaked; they will evolve over time as we receive and analyze more and more performance data.

 


 

Performance Score

The Performance Score is essentially your Lighthouse Performance score, as captured by GTmetrix tests, with our browser, hardware specifications, and specified Analysis Options (AdBlock, Connection Speeds, etc.).
 

The Performance Score tells you how well your page performs from a user perspective.

This score is made up of 6 key metrics with the following weights:
 

 
Each metric is measured and calculated as a score, then compared to a threshold, and the aggregate result (with the appropriate weighting) makes up the final Performance Score.

Complete details of your Performance Score are listed in the Performance Tab of the GTmetrix Report.
 
 

How does this compare to the Performance score I see on Google PageSpeed Insights or web.dev?

While the official Google tools are also driven by Lighthouse, they use their own hardware and testing methodologies to generate the Performance score.

Here are a few key differences that would make the scores vary:

  • Geographic differences
    It’s unknown if Google does tests in servers based on their geographic region. GTmetrix allows you to define which test region to analyze your page from.
     
  • Hardware differences
    GTmetrix and Google will likely have different CPU/Memory designations for tests, which will affect the metrics.
     
  • Network differences
    Differences in network connections and variances may contribute to changes in individual metrics.
     
  • Other Google-magic
    Google may have additional considerations when calculating the Performance score (e.g., Lantern for CPU/Network throttling).

 
While the GTmetrix Performance Score and Google generated Performance scores are not directly comparable, they should be similar.

Click here to learn more about how the GTmetrix Performance Score compares to other Lighthouse based tools.

 


 

Structure Score

The Structure Score is our own proprietary assessment of Lighthouse Opportunity and Diagnostic audits.
 

The Structure Score tells you how well your page is built for optimal performance.

We’ve taken these audits and assigned point values to them based on various factors, including potential savings and importance, as perceived by the GTmetrix team.

See a complete list of these Structure audits listed here.

Similar to the PageSpeed and YSlow scores in the Legacy Report, how well you do on your Structure Score is reflective of how well your site is built for optimal performance.
 
 

Our Custom GTmetrix audits

In addition to the standard Lighthouse audits, we’ve also included our own custom audits that we deemed relevant to web performance. These custom GTmetrix audits include:

  • Enable Keep-Alive
    • This will only trigger on pages using HTTP/1.1 with no Keep-Alive ON directive detected.
    • If your page is detected to be using HTTP/2, this audit won’t affect you.
       
  • Combine images using CSS sprites
    • If your page serves multiple small, spritable images, this audit will be triggered.
    • Note that this audit has different thresholds depending on whether your page uses HTTP/1.1 or HTTP/2.
       
  • Use a Content Delivery Network (CDN)
    • We’ve discussed the benefits of CDNs in past articles, and still feel they play an important role in delivering a consistently fast website, worldwide.
    • While not as penalizing as it once was in Legacy Reports, GTmetrix will continue to flag any static resources that could be served on a CDN for better global delivery.
       
  • Avoid CSS @import
    • Avoiding CSS @import when possible is still a recommended practice as any import directives encountered by the browser (without the defer attribute) will be immediately downloaded, parsed, and executed.
    • This can block rendering of the rest of your page.

 

Complete details of your Structure Score are listed in the Structure Tab of the GTmetrix Report.
 
 

Do my Structure Scores affect my Performance Scores?

Your Structure Scores do not directly affect your Performance Scores.

However, improving your Structure Score can generally improve your page performance, overall. This would result in better Performance Scores, and by extension, a better GTmetrix Grade as well.

Think of the Structure audits in the new GTmetrix Report as the instruction manual for better web performance, and the Performance Score metrics as the stopwatch of your actual web performance.
 

A high Total Blocking Time is likely due to long main-thread tasks and JavaScript execution.

 

Addressing the Structure audits can serve as a good starting point to improve page load times overall. Additionally, some of the audits are correlated and thus, fixing one audit may affect others.

 


 

Web Vitals

Google has established Web Vitals as the core metrics that you should focus on to deliver a fast website experience.
 

Web Vitals are key metrics that impact your page’s performance the most.

 
These metrics include:

 
Doing well on these metrics is a good indicator that you are delivering a fast and (what Google calls) a delightful experience to your visitors.

Web Vitals are a great way to benchmark your page as they focus on a small set of key metrics that are most impactful to the perception of performance; you’ll find Web Vitals front and center, alongside your GTmetrix Grade and Performance/Structure Scores in the new GTmetrix Report.

Learn more about Web Vitals on our documentation page.
 


 

New Summary, Performance and Structure Tabs

This new release brings forth a revised GTmetrix Report with new tabs. We detail each of the tabs below:
 


 

The Summary Tab

New to GTmetrix Reports is the Summary Tab, which shows you a complete snapshot of your page’s Performance, Structure, and load behaviour.

Consider this tab your primary action center, as the information here alone can be enough to to provide significant direction in improving your page’s performance.
 

The new GTmetrix Summary Tab

 
At the top of the Summary Tab is our new Speed Visualization, an intervaled capture of your page load, with flags that mark your various Performance Score metrics as your page loads.

This gives you more context on the metrics in relation to what your visitors actually experience.
 

Your Performance Score metrics are paired with an intervaled capture of your page load in our new Speed Visualization.

 
Next, you’ll see the primary Structure issues that contribute the most to your page’s performance in our Top Issues section.
 
Focus on these Structure audits first as they impact your page performance the most.

 
Focusing on improving these audits first can have a cascading effect on your other Structure audits, and can drastically improve your overall GTmetrix Grade and Performance/Structure Scores.

As you improve audits shown here, you’ll find that new audits appear on the Top Issues section as you retest; this allows you to prioritize optimization efforts based on their impact on your page’s performance.

Below Top Issues, you’ll find a new Page Details graph that shows what types of requests your page is comprised of, including the number of requests and byte size they make up.
 

The Page Details graph shows you how your page is composed in terms of request size and types.

 
This is useful for determining at-a-glance if your webpage is heavy on JavaScript, CSS, images, etc. Hovering over a segment shows you additional information on that request type as a whole.
 
Hover over each segment to get additional details on the request type.

 
Lastly, you’ll find a More from GTmetrix section, where we provide optimization tips and advice based on your page analysis.
 
Get articles and tips from GTmetrix based on our analysis of your page.

 
Depending on what we detect during the testing of your page, we may offer tips and guidance on your platform (i.e., WordPress, Shopify, etc.), image optimization, server performance, CDN usage, etc.

 


 

The Performance Tab

We’ve retired the Timings Tab and replaced it with the new Performance Tab, which shows you your Performance Score metrics in detail.
 

The new GTmetrix Performance Tab.

 
Each metric comes with a brief description (so you know what it means at-a-glance) and is colour-coded depending on how your page did in that metric.

We’ve done our best to give you a little more context on how your metric did, with more verbiage that reflects the impact of that metric on your page performance.
 

You can hide metric details for a data-only view of your Performance Score metrics.

 

If you wish, you can hide descriptions for a cleaner, unobstructed view of all your metrics.
 

Colour-coding and context

Depending on how the metric performed, you’ll see the following colours and messaging:
 

Each metric is accompanied by a colour-coded description to help you understand its impact.

 
Below the Performance Score metrics, you’ll see your Browser Timings, the same ones you remember from the Legacy GTmetrix Reports.
 
Browser Timings (i.e., timings from the previous Timings Tab in Legacy GTmetrix Reports) are included in the Performance Tab.

 
Browser Timings have no direct impact on your Performance Score; however, they may provide additional insights on your page performance and are worth reviewing.

 


 

The Structure Tab

The Structure Tab is the spiritual successor to the PageSpeed and YSlow tabs, containing all of your Structure-based Lighthouse audits and best practices for optimal web performance.
 

The new GTmetrix Structure Tab.

 
You’ll see a familiar table-based layout with all of the Structure audits organized by how well you adhered to them, with the worst performing audits listed at the top.

New to GTmetrix is Impacts for audits – a proprietary assessment consisting of potential savings, impact on metrics and other considerations.

The Impact essentially represents how much the particular audit impacted your Performance Score.

Impacts are calculated based on analysis findings, then placed in one of the following thresholds:
 

Impacts denote how much the Structure audit affected your Performance Score metrics.

 
Your aggregate Impacts from each audit are calculated to form your page’s Structure Score.

Clicking on each audit will expand it, revealing the requests that contributed to the audit’s Impact.
 

Clicking the audit will display the resources that are render-blocking.

 


 

Other Tabs

The rest of the GTmetrix Report Tabs generally remain intact with few changes:
 

  • Waterfall Tab
    • The GTmetrix Waterfall Chart sees no change in this release and provides an excellent companion to the Lighthouse data.
       
  • Video Tab
    • The Filmstrip that was previously in the Video Tab has been removed in place of the Speed Visualization on the Summary page.
    • While the video player sees no changes – note that the video player legend does not have the new Lighthouse milestones implemented yet (coming soon).
       
  • History Tab
    • Changes in the History Tab include the addition of new graphs for Performance Score metrics and the replacement of PageSpeed and YSlow graph with the GTmetrix Grade/Performance and Structure Scores graph.

 
Note that you can still view your PageSpeed/YSlow performance history if you view a previously generated Legacy GTmetrix Report.

 


 

How does the new GTmetrix Report compare to the Legacy Report?

For the most part, it doesn’t.

The Lighthouse-based metrics used to generate the new report are fundamentally different compared to the previous PageSpeed and YSlow Recommendations. While both reports share a few timings, they should not be a one-to-one comparison.

As the testing methodology and metrics have changed, you should consider the new Lighthouse-powered GTmetrix Reports as a new benchmark for your pages.

The new GTmetrix Report represents an all-new benchmark for site owners to assess web performance.

The Legacy Report provided recommendations based on how well they adhered to PageSpeed/YSlow best practices, i.e., they only focused on the Structure or how well your page was built for speed.
 

The Legacy Report primarily focuses on Structure while the new GTmetrix Report focuses on, both, Performance and Structure.

 

The new GTmetrix Report, however, focuses on, both, Performance and Structure i.e., how well your page actually performed (loading, interactivity, visual stability) for a user, as well as, how well your page is built for performance.

Overall, the new GTmetrix Report sets an entirely new web performance standard for your pages as it focuses on your page’s user experience.

 


 

Summary

This is the most comprehensive update to GTmetrix yet and we’ve worked very hard to bring you a product that is well-suited to your web performance needs.

The new GTmetrix Report has been completely redesigned to accommodate the new Lighthouse data, which will likely change the way you assess your page performance.

Refer to our documentation to learn more about the Structure audits and the Performance Score metrics, and have a look at our blog to learn more about the new Lighthouse-powered GTmetrix in general.

 


 

You can read more about the new GTmetrix platform and other associated changes in the following articles:

 


 

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