Introduction
Over the last years most digital marketers were likely overwhelmed by the concept of Server-side (SS) Tagging. Facebook has been spamming our inboxes, shouting the urgency of implementing their Facebook CAPI solution, and also Google has been paving the way by creating a Server-side solution for GTM that easily integrates within their own Google Cloud Platform.
Working SS has plenty of advantages: At first, the server response could write first-party cookies to bypass technical privacy measurement such as Ad Blockers or Apple’s ITP, but as we moved forward we learned that this is not the main selling point. More importantly SS Tagging grew in importance within the story of compliance and governance. Owning your data is gaining attention, so you are in control of what is being sent to your digital platforms (such as GA4, Meta, Pinterest, etc).
Another, perhaps less popular, argument to move your tracking to a server-side environment, is that it improves the page speed by reducing the load on the browser. In this article we focus on the empirical evidence regarding the latter one. If you want to read a more general overview of the advantages of SS Tagging, I highly recommend you to check out this article written by my colleague Margaux Marien.
Why is page speed important?
This sounds like a no-brainer. Page speed is crucial and in strong correlation with SEO, user experience, and on-site conversion rates. In other words, if you care about the performance of your website, page speed will play a crucial role for your business. According to Google research, if a site takes longer than 3 seconds to load, 53% of users will leave. On top, we noticed that the attention span of the average user is only getting shorter and shorter (look how TikTok has been booming!) so let’s not risk putting their patience to the test.
How do tags impact page speed - The theory
Typically, technology partners require you to add their JavaScript code (known as 3rd party tracking tags) to your website so that their platform can effectively track campaign performance. Each tag you add to your site (through GTM or any other TMS) performs another HTTP request. So when a tag makes a call to a third-party server, valuable seconds are added to your load times.
In fact, Pingdom’s study has shown a big difference in page speed between website that are using tracker tags vs websites that don’t. This research has been performed on the 50 biggest news websites.
Stunningly, the average page speed drops from 9.46 to 2.69 seconds for publishers that don’t work with trackers. The study also outlined that 82% of all tags are advertising tags.
Thus by moving your 3rd party tags away from your website and into a server container, you reduce the amount of JavaScript processed and outgoing HTTP requests, which will likely improve website loading speeds. This way, the page will load faster, and it will have a positive effect on the user experience.
Well sure, but does it really?
Let’s step away from the theory and put things into practice. Firstly, Stape.io tested it out by using the Google PageSpeed results and they saw their website’s performance score increase from 56 to 95 points when moving away from client- to Server-side GTM. The test ran in a mobile environment only. You can read all the details here.
But being Semetis, we wanted to take matters into our own hands and prove it for ourselves. For our research we set up a test where we calculated the page speed before and after implementing SS GTM. We used webpagetest.org and pagespeed.web.dev as our sources of truth and scheduled multiple tests on both mobile and desktop.
The conclusions are clear: in our cases switching to SS GTM had a big impact on page speed.
All our metrics are measured in seconds (except the Mobile Performance Score). Over the full line our speed metrics have significantly improved. The Core Web Vitals (LCP and TBT) have been reduced by respectively 23% and 60%. Also the overall Mobile score went up from 59 to 68! Our tests performed better on both mobile and desktop, even though the largest Contentful Paint metric improved significantly better on desktop vs. mobile.
So to answer the question: "Does moving to SS GTM positively impacts page speed?" Yes it does! So if you weren’t convinced about this technology before, we hope you are now.
Keep in mind that we didn’t run this test on many websites. The results are significant but not conclusive. More tests will need to be deployed as page speed is impacted by various factors. These results will massively vary depending on the amount of tags you have, and not all tags are equally heavy. Nevertheless, based on today’s results, the future looks promising.
Don’t hesitate to reach out to Semetis if you need assistance with the implementation. We are happy to advise.
Frédéric Palella
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