The GTmetrix Speed Test Tool: A Detailed Guide

GTmetrix provides a free page speed testing tool to check your website performance. Find out how it works, how to interpret its performance recommendations, and what other tools you can use to test your website speed.

What is the GTmetrix Speed Test?

GTmetrix's website speed speed test is a free tool that you can use to measure the loading speed of your website. Just go to gtmetrix.com, enter your website URL, and click Test Now.

GTmetrix will open your website in Chrome, collect performance metrics, and scan for potential improvements.

Once the test is complete, GTmetrix provides the following details at the top of the report:

• An overall letter-based GTmetrix grade
• The Lighthouse performance score
• A Structure score
• Your Core Web Vitals metrics: LCP, TBT, and CLS

Altogether, this doesn't tell us too much. You can create a free account to get more information – we discovered we needed to run the test a second time once we'd logged in.

tip

Don't want to sign up for GTmetrix? DebugBear's free speed test gives you all the results you need without requiring an email address.

Running a full test once logged-in

You can run up to five tests before you need to pay. Once logged-in, you can adjust some of the options (although not as many as paid users can) such as server location, network speed, and whether you want video or ads enabled or disabled.

Choosing a server nearer where your audience tends to connect from may give you a more realistic result.

Full GTmetrix test results

Once this test has run, you'll receive a more substantive report with actionable advice.

Beneath your headline speed stats, you'll see a filmstrip showing how your page loaded step-by-step.

Below that, you'll also discover a set of advisory notices – the Lighthouse recommendations you might recognize from PageSpeed Insights.

On the right, a graph gives you an overview of your page size and the number of server requests being made.

But that's not all – you can explore the tabs along the top of the page to reveal further information.

• Performance reveals 17 page speed metrics, from Time to First Byte to Fully Loaded Time.
• Structure presents even more page speed recommendations, in priority order.
• CrUX shows the latest information on this URL from Google's CrUX dataset
• Waterfall depicts a detailed chronological breakdown of every single page resource and request
• Video (if you enabled it) presents a slowed-down visualisation of your page loading
• History provides comparative data (if you've tested this URL before)
• Alerts allows you to set up monitoring and get notifications if page speed declines

Performance metrics

This part of the GTmetrix report shows you how your website scores on a number of web performance metrics.

Toggle the Metric details option to view an explanation of how each metric is collected.

Request waterfall

The request waterfall tells you when the browser loads different page resources during the loading process.

Loading a website always starts by loading an HTML document which then references stylesheets, JavaScript files, web fonts, and other resources that are necessary to display page content.

You can hover over reach request bar to see a more detailed breakdown of the request duration:

1. An HTTP server connection is created (DNS / Connecting / SSL)
2. The resource request is sent and processed by the server (Sending / Waiting, measuring theTime to First Byte)
3. Receiving, which means downloading the full response body

Click on a request to expand it and view details like the HTTP request and response headers.

• content-encoding tells you whether HTTP compression with Brotli or GZIP was applied by the server
• cache-control and expires tell you how long the resource can be stored in the browser cache

tip

The DebugBear request waterfall provides additional insights to help you better understand how each resource impacts page speed.

GTmetrix test recommendations

GTmetrix draws upon insights from Lighthouse, as well as a few of their own, to help you improve your page load speed.

Here's what the recommendations are and how they can help your website speed. We have articles on many of these common website speed audit insights that walk you through the changes you need to make.

1. Allow back/forward cache restoration – ensures the page doesn't unnecessarily re-download content when the user visits by hitting the back button in their browser
2. Avoid an excessive DOM size - reduces the complexity of the page structure, helping the brwoser render it faster.
3. Avoid chaining critical requests - simplifies the network dependency tree so important files get downloaded faster
4. Avoid CSS @import – uses a more efficient method for loading CSS.
5. Avoid document.write - this can delay the display of page content by tens of seconds and is particularly problematic for users on slow connections
6. Avoid enormous network payloads - improve page download speeds by reducing the size of files needed to render the page
7. Avoid large layout shifts - improves the page so the content doesn't seem to 'jump around' as additional scripts, fonts and images are loaded
8. Avoid multiple page redirects - reduces the number of server requests the browser needs to make
9. Avoid non-composited animations - prevents stuttering movement on low-resource devices like old smartphones
10. Avoid serving legacy JavaScript to modern browsers - eliminates unnecessary downloads and parsing of irrelevant code
11. Eliminate render-blocking resources - stops Javascript and CSS in the head delaying page content being displayed
12. Enable Keep-Alive - gets the user's browser to 'stay connected' to your server rather than starting a new connection with every request
13. Enable text compression – reduces file sizes with GZIP or Brotli compression
14. Ensure text remains visible during webfont load - add font-delay: swap to display text in a system font while the web font is still downloading
15. Lazy load third-party resources with facades – improves performance by lazily-loading an image rather than a full piece of embedded, until the user is ready to interact with it
16. Minify CSS and Minify JavaScript - makes code download faster by removing every unnecessary character
17. Minimize main-thread work and avoid long main-thread tasks - frees up the main processing thread to actually render the page and process interactions
18. Preconnect to required origins – establishes a connection to relevant servers in advance of needing to download content from them
19. Reduce initial server response time – use a faster web host or condent delivery network to accelerate loading
20. Reduce JavaScript execution time - frees up the main thread for content rendering
21. Reduce the impact of third-party code - limit the number of plug-ins and resources from other domains, like analytics, ads and chat services
22. Reduce unused CSS and reduce unused JavaScript - improves page speed by discarding unnecessary code
23. Serve static assets with an efficient cache policy - encourages the user browser to serve cached assets rather than re-downloading them
24. Use a <meta name="viewport"> tag with width or initial-scale - enables mobile browsers to display your page optimally
25. Use a Content Delivery Network (CDN) - have copies of your site served from geographically local servers
26. Use HTTP/2 for all resources - allows the user's browser to make multiple server requests at once over the same connection
27. Preload Largest Contentful Paint image - makes downloading the most prominent image on your page a top priority
28. Efficiently encode images - reduces the file size of image resources without visible reduction in quality
29. Use explicit width and height on image elements - prevents jumps in layout by holding space for yet-to-be-loaded images
30. Combine images using CSS sprites - reduces the number of server requests by combining many small images into one
31. Defer offscreen images – postpones loading images that are out-of-sight until later, freeing up bandwidth for above-the-fold content (also known as 'lazy loading')
32. Use passive listeners to improve scrolling performance - eliminates delays when the user starts to scroll
33. Use video formats for animated content - eliminates over-large animated GIFs with more efficient video formats
34. Serve images in next-gen formats - reduces image download size by using WEBP and AVIF compression
35. Properly size images - avoids delivering unnecessarily high-res images for users on smaller mobile devices
36. Don't lazy load Largest Contentful Paint image - accelerates the download of your most high-priority image

tip

Not sure where to start? Read our guide on how to improve website performance!

Google CrUX data

GTmetrix normally runs synthetic tests where data is collected on-demand in a controlled lab environment on a GTmetrix server.

However, it can also report real user data from Google's Chrome User Experience Report (CrUX).

This tells you whether your website passes Google's Core Web Vitals assessment, which impact how your site ranks in search results.

Other speed testing tools

There are many site speed testing tools available online as alternatives to GTmetrix. If GTmetrix doesn't offer the data you need, try out DebugBear's free website speed test.

You can test pages on mobile and desktop devices, measure Google Core Web Vitals, and investigate when different page resources load.

If you have a DebugBear account, you can also run experiments to measure the impact of a change without making any changes to your live website.

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Track your page speed over time

If you're working on your website performance you can set up continuous synthetic monitoring for your pages to confirm your optimizations are working and get alerted to any regressions.

You can also set up real user monitoring (RUM) to see how fast your website is for actual website visitors, and what you can do to fix that.

RUM data can tell you:

• If specific visitor segments have a slow experience
• How page interactions cause poor performance
• What pages across your website are slow

If you're struggling with poor Interaction to Next Paint scores, DebugBear RUM can tell you where on the page those interactions are happening and what scripts are slowing them down.

Monitor Page Speed & Core Web Vitals

DebugBear monitoring includes:

• In-depth Page Speed Reports
• Automated Recommendations
• Real User Analytics Data

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