GTMetrix: the complete guide

Page load speed is one of the criteria that determine a site’s quality. That is why it also plays a role in the position Google gives the site in the search results pages (the SERPs). The stakes are high: a slowdown of a few fractions of a second can cost you ranking, traffic, and revenue. If you are optimizing organic search to grow the business, the first useful reflex is to analyze how fast your site loads and take corrective action if needed. That is where tools that measure speed and display performance, such as GTMetrix, come in. A closer look at this handy SEO tool.

Preamble: identifying what slows a site down

If you are not bilingual, GTMetrix is still usable by anyone, and this guide exists to prove it. The actions you then take to get results do require some knowledge of code and how a site is built. At a minimum, you will need a developer to implement the recommendations from the GTMetrix analysis. That analysis focuses on the causes of a slowdown, and there can be several.

Ads, images, and Flash

The performance of a website’s pages depends on a large number of factors. In some cases, a high number of HTTP requests caused by too many ads or poorly optimized images creates problems. In general, the heavier or higher-resolution the assets, the heavier the page. When too many requests go out at once, you can get blocking or slow processing. GTMetrix lets you run tests with or without the ads on a page, so you can see their impact on load time. Flash, useful as it once was for interactivity, is a well-known source of slowdowns. Webmasters have since moved to HTML5. Flash on older sites can still be a real cause of slowness, and it is strongly discouraged.

Technical issues: encoding, scripts

In other cases it is a more technical problem with JavaScript or HTML, or a deeper issue tied to the CDN, the content delivery network. It is often hard to pinpoint exactly what is slowing a site down. Whatever the origin, it is worth analyzing your site to improve performance, and GTmetrix helps you see more clearly.

How does GTMetrix work?

Creating a free account

GTMetrix is a tool with many features available for free. You can go to its web interface and test your site right away. Signing in gives you more options for test-server location and a few other settings. With a user account you can also automate regular reports.

The premium account

A GTMetrix premium account includes video analysis (a slow-motion recording of the page loading, one resource after another) and test history. It also lets you view the results of several tests on a single page. The chart it offers makes the data easier to read.

GTMetrix speed test

On a GTMetrix test, the results page shows the context and settings of that test: the browser used and its version, the server location, the PageSpeed score and the YSlow score. It also shows how many requests the page load generates, the page weight, and the total time to load. Those figures, highlighted and pre-interpreted with a color code, give a first look at the page’s overall performance.

PageSpeed and YSlow

Complementary indicators

PageSpeed and YSlow are two different, complementary indicators in page analysis. Each is an average, expressed as a percentage, of several criteria. Each indicator has its own tab that lists the criteria it is made of, ranked in ascending order (the lowest scores are the most problematic points in the analysis). A color code also lets you see at a glance how important a criterion is among the causes of slowness.

PageSpeed and YSlow give you the list of criteria they are built from, and a score from 0 to 100 for each. They look at things such as Gzip compression, minifying resources, optimizing image size, the size of JavaScript and CSS assets, and the presence of 404 headers.

Each criterion points to the exact blocking items and gives concrete recommendations to apply on the site. You see, for example, which assets are judged too heavy and how much they weigh, along with a note on what to do or what target to hit (a 15% reduction, for instance).

GTMetrix’s other tools

The Waterfall

The Waterfall is a GTMetrix feature that lets you locate the exact slowdown points of a page by following the cascade of resource loading. Every request made during the load is shown one after another as a bar that represents its duration. Hovering over each bar shows detailed information on how that load time is composed.

Here are all the stages a resource load can go through:

• DNS lookup: the time spent finding the DNS

• Connection: the time needed to open a connection

• Blocking: the time spent in the browser queue

• Sending: the delay before the request is sent

• Waiting: the time spent waiting for the response (time to first byte)

• Receiving: the time needed to download the content

Timings and time to first byte, or TTFB

The cascade view also offers vertical, colored markers that correspond to strategic points in the page load: the blue vertical line is the moment the DOM (Document Object Model) is loaded, the programming interface that lets scripts inspect and change the content of the web browser. The red line is the exact moment the page finished loading. Together, these data give you a closer look at how your page loads and how each resource behaves on the way to the overall load time.

The Timings tab gives you a summary of those precise timings. Pay attention in particular to time to first byte (TTFB), or how fast the first byte is sent, because it gives you an idea of your server’s speed. If your TTFB stays high even after your other optimizations, you probably need to push the analysis toward the server.

Measuring a site’s performance

Running several tests

GTMetrix is an effective SEO tool for measuring how long a site takes to load. It lets you run tests in several configurations by changing parameters such as connection speed, device, screen resolution, and server location. A test result is only valid for the configuration you chose, so it is better to run several tests with different settings to get an average, realistic load time.

It is also a good idea to pick those settings based on how your users actually browse: with Google Analytics, you can see which devices your visitors use most (smartphone brand and model, for example), which browsers they prefer, and where they are located. That lets you customize your tests so they are as representative as possible of the real user experience.

To multiply these tests and make sure they are reliable, spread them over a program of at least one week. Schedule tests across several time slots in the day, so you can account for seasonality or catch peak hours. A site’s performance changes throughout the day and often tracks its traffic peaks.

From the data recorded in these different tests, you will be able to identify the slower periods for your site, and GTMetrix will give you recommendations and scores on each audited point: image optimization, the state of the JavaScript, CSS stylesheets, HTML, and more. You can also set up a regular report in the most common configuration, and GTMetrix lets you export it as a PDF, compare it with others, and so on.

Configuring the tests

Choosing test servers

The risk with most free load-time tests is that the geographic location of the server is random. As a result, the results for a site hosted in France and tested from a server in Australia cannot be treated as reliable if the site has no content delivery network (CDN). To get better tests, pick relevant servers on GTMetrix, ones that let you test the site in the conditions your users actually use.

Choosing geolocation

You need to know where your server is before you run the tests. If needed, ask your domain name provider. Configure the tests by choosing servers in the geographic areas where your targets and prospects are.

Choosing target pages

To test a site’s load time, start with the homepage, then focus on your strategic pages, the ones rich in content that appear in the SERP on high-stakes keywords. Those are the pages that contribute to the site’s traffic. You can also focus on the landing pages of the most business-oriented queries (pulled from Analytics). That gives you a view of the main pages people use to enter your site, and you can judge the quality of their user experience. Our SEO agency can help you optimize your site’s SEO performance.

Choosing advanced options

GTMetrix offers advanced settings and deep customization of some test configurations. You can force another DNS, which is useful for testing development environments or during migrations. You can analyze password-protected versions of a site by entering the credentials in the tool. You can analyze pages that require the user to be logged in, using a customizable list of cookies. Finally, you can provide two lists of approved or blocked (blacklisted) resource URLs so they are shown or hidden on the page, and therefore included or excluded from the load-time calculation.

In short, GTMetrix is a fairly complete tool even in its free version, and it covers the criteria that go into page load time and display. It lets you run precise, realistic tests against your actual audience, identify the heaviest resources, and pick the priority actions to improve this crucial KPI: load speed. Use it regularly to check that your optimizations are working, and watch your organic search improve little by little.