Server-side vs. client-side tracking: Differences, benefits & the GDPR

What is client-side tracking?

Client-side tracking is the traditional and most widely used method of measuring user behaviour on a website. Here, data collection takes place directly in the user’s browser – typically via a pixel or a script from, for example, Google Analytics, Meta or LinkedIn, which is embedded on the page via Google Tag Manager.

When a user clicks, makes a purchase or fills in a form, the browser sends data directly to third-party servers – bypassing your own infrastructure. It’s quick to set up, but it also means that, in practice, you’re handing over control of the data to the browser, ad blockers and the third party’s own rules.

What is server-side tracking?

What is server-side tracking, in a nutshell? It is a method whereby data is sent from the browser to your own server – typically a server-side Google Tag Manager container (sGTM) – which then cleans, enriches and forwards the data to Google, Meta and other platforms.

In practice, this means that your server acts as an intermediary. Instead of the website having a large number of direct connections to third-party scripts, the data passes through a single controlled point over which you (or your agency) have control.

Advantages of server-side tracking

When companies switch from purely client-side to server-side tracking, it is typically these benefits that drive the decision:

• More accurate data. Ad blockers and browser restrictions (such as Safari’s ITP and Firefox’s ETP) largely block client-side scripts – but have a much smaller impact on server-to-server communication.
• Less data loss. Because tracking does not rely on the user’s browser allowing third-party scripts, you’ll miss fewer events – particularly conversions and purchases.
• Better performance. Fewer scripts to load in the browser mean faster page loading times and a better user experience.
• Greater control over data. You can filter, anonymise and enrich data before it is passed on – for example, by removing sensitive parameters or hashing personal data.
• A better basis for ad optimisation. More comprehensive data provides Google’s and Meta’s algorithms with a better basis on which to optimise your campaigns.
• Simpler GDPR compliance. Because the data passes through your own checkpoint, it is easier to ensure that only data for which consent has been given is forwarded.

Client-side tracking and the GDPR

Client-side tracking poses GDPR challenges, typically because data is sent directly from the browser to third parties without an intermediary through which you can check what is actually being sent. This makes it more difficult to:

• Ensure that only data for which consent has been given is actually passed on
• Filter out sensitive information before it leaves your site
• Document precisely which data has been shared with which platforms
• Comply with the data minimisation requirement (Article 5(1)(c) of the GDPR)

However, it is important to make it clear that server-side tracking is not a loophole that exempts you from consent requirements. Whether you use client-side or server-side tracking, you must still obtain valid consent before collecting and sharing data about your visitors – server-side tracking does not alter the fundamental obligation to obtain consent, but provides you with better tools to comply with it.

How server-side tracking supports the GDPR in practice

Combined with a consent banner and Google Consent Mode v2 Server-side tracking can actually make it considerably easier to comply:

• Data storage in the EU. The server can be located in the EU (e.g. Amsterdam or Paris), which meets the Danish Data Protection Agency’s requirements for data transfers.
• Data Processing Agreement (DPA). As the data is processed via a specific server, it is clear who the data processor is, and a data processing agreement (DPA) can be entered into directly.
• Controlled data minimisation. You can specify exactly which fields are passed on – for example, hashing email addresses (SHA-256) and truncating IP addresses before they leave your server.
• Respect for the right to choose. When a user opts out of cookies, you can still pass on aggregated, anonymised conversion data – without storing cookies on the user’s device.

Tracking without cookies – is it possible?

Tracking without cookies has become a key priority for many businesses, as browsers tighten restrictions on third-party cookies and more users actively opt out of giving their consent. Server-side tracking is one of the methods that makes this possible in practice:

• Conversions can be tracked via first-party connections rather than third-party cookies
• When a user opts out of cookies, aggregated and anonymised behavioural data may still be collected – without any cookies being stored on the user’s device
• Google Consent Mode v2's "advanced mode" can be used to send anonymous signals that improve data modelling, even without full consent

It is important to understand that cookie-less tracking does not mean tracking without rules – it means that one relies to a greater extent on aggregated and modelled data rather than individual user tracking via cookies. This makes the solution more future-proof as both browsers and legislation tighten restrictions on cookie-based tracking.

What exactly is server-side GTM?

Server-side GTM (Google Tag Manager) is the engine that enables server-side tracking. Instead of your standard (client-side) GTM container sending tags directly from the browser, you create an additional, server-side container, which acts as a receiver and distributor of data:

1. The browser sends data to your server-side GTM container rather than directly to third parties
2. The container processes data – for example, by adding, removing or anonymising parameters
3. The container forwards data to the relevant platforms (Google Ads, Meta, GA4, etc.) via server-to-server connections
4. The entire process is logged, so you have a complete overview of what is being sent and where

The technical setup typically requires cloud hosting (e.g. Google Cloud), correct domain configuration and ongoing monitoring – which is exactly what an agency or a subscription service such as WeTrack takes care of for you.

Are there any drawbacks to server-side tracking?

Server-side tracking is not a one-size-fits-all solution, and it is worth being aware of the drawbacks before you proceed:

• Technical complexity. The setup requires more technical knowledge than a standard client-side installation.
• Day-to-day operations. The server must be operated and monitored to ensure that tracking does not break when platforms change their requirements.
• Cost. There is usually an ongoing cost associated with hosting and maintenance – although this is often recouped through improved data quality.
• Consent is still required. As mentioned, server-side tracking does not exempt you from the requirement for valid consent – it does not, on its own, fulfil your GDPR obligations.

For most businesses with a reasonable advertising budget, however, the benefits clearly outweigh the drawbacks – particularly because the data lost through client-side tracking alone often costs more in poorly optimised adverts than a server-side solution costs to run.

When does what make sense?

As a general rule of thumb:

• Client-side tracking may be sufficient for very small websites with low levels of traffic and advertising, where data loss does not have a significant financial impact.
• Server-side tracking offers the greatest value to online shops and businesses that spend a substantial advertising budget on Google Ads or Meta, and where data quality has a direct impact on the bottom line.

Many companies end up adopting a hybrid approach: a continued client-side setup for basic analytics, combined with server-side tracking specifically for conversion data, where accuracy is paramount.

Frequently asked questions