In analytics, server-side and client-side tracking are the methods used to transmit data collected from a browser to an analytics platform.

In client-side tracking, the collected data is sent directly to the analytics instance.

It’s the most popular technique for collecting analytics data. The method is also well documented and doesn’t require advanced technical skills. But it has limitations. Client-side trackers are easy to detect and disable for popular ad blockers. Because of that, some companies turn to other methods that ad blockers won’t affect, such as server-side tracking.

In the server-side method, the collected data is sent to a server that hosts your website or app, and then passed to your analytics instance.

Server-side trackers, also known as first-party collectors, are undetectable in browsers. Because of that, they’re not blocked by ad blockers. They also help you avoid limiting the lifespan of cookies or detecting CNAME Cloaking by tracking prevention mechanisms, such as Safari’s Intelligent Tracking Prevention (ITP) or Firefox’s Enhanced Tracking Prevention (ETP).

Using a server as a reverse proxy allows companies to fully control what kinds of data enters their analytics platform to, for instance, eliminate any traces of personal data or mask user IPs.

That said, companies that use server-side tracking to collect personal data need to carefully document the tracking methods they use in their privacy policies. They also need to obtain lawful visitor consent for personal data collection, just as they would do if they were using client-side trackers.