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Digital tracking
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What is server-side tagging – and why do you need it?

The era of reliable client-side tracking is ending as browser restrictions and privacy regulations decline the utility of third-party cookies. Server-side tag management is the critical next step, offering a more robust, secure and efficient method to maintain your strategic advantage in digital measurement.

Sarah Crooke
Sarah Crooke

18 December 2025

6 minute read


More clients these days have been asking about server-side tagging. This generally comes up first when marketing has told them to implement Facebook CAPI. Though this may seem like a quick and easy pixel implementation, it is actually a complete shift in how your tracking can take place. CAPI and other analytics tools are moving towards server-side tag management, which provides a more robust, secure and efficient method that represents your next significant strategic advantage.

What is wrong with the old ways?

For years, client-side tagging has been the default method for digital measurement. It involves placing numerous JavaScript tags directly on a website, which then communicate from the user's browser to various third-party vendors. While straightforward, this model:

  • sometimes relies on third-party cookies
  • adds load time to your website 
  • doesn’t adhere to GDPR privacy regulations (the only choice is to not send the data)
  • doesn’t allow for methods to enhance your data across multiple systems. 

The decline of third-party cookies

The digital marketing attribution method was built on third-party cookies. These small files, placed on a user's browser by external domains, enabled cross-site tracking, ad targeting, and attribution. However, their era is ending. Major browsers like Safari and Firefox already block them, rendering much of the client-side tracking infrastructure obsolete.

Browser restrictions and the rise of tracking prevention

Modern browsers are increasingly equipped with sophisticated tracking prevention technologies, such as Apple's Intelligent Tracking Prevention (ITP). These tools actively limit the lifespan of cookies and block requests to known tracking domains. This direct intervention by the browser means that a significant portion of client-side tracking data is lost before it reaches its destination, creating critical gaps in analytics.

Though we should always honour a user's right if they don’t want to be tracked, and no analytics platform is 100 percent accurate, server-side tracking does help with filling in some holes.

The imperative of privacy regulations and user expectations

Regulations such as GDPR and CCPA have codified consumers' right to privacy, imposing strict rules on data collection and consent. The client-side model, which often sends a broad spray of user data directly to countless vendors from the browser, makes it exceedingly difficult to govern and control this flow, increasing compliance risk. This may seem like a problem for people marketing in Europe, but Australia has been reviewing the laws for the past few years, and changes appear imminent. Current guidelines are closer to the EU than you think. 

Understanding server-side tag management

Server-side tag management, often called server-side tagging, can still rely on your regular tagging solution (such as Google Tag Manager). Still, instead of sending data directly to the marketing platforms, it goes via a server. This server can transform the data and send it to the relevant platforms. 

In client-side tagging, the user’s browser does all the work. Each tag loads and executes JavaScript, collects event data, and sends it directly to vendors such as Google Analytics or Meta. In server-side tagging, the browser sends a single, consolidated data stream to a server you control. This server then processes, enriches, and distributes the data to your vendors, acting as a secure intermediary.

To understand the benefits, let’s look at an example. A lead comes through on your website:

  • Client-side GTM has a single script that sends lead data to the server-side, instead of loading scripts for each marketing platform, which slows the site.
  • The client will send it to a server with your own domain, making it a first-party cookie and also less likely to be blocked by ad blockers.
  • Server-side GTM gets the data of this lead, so we can then:
    • strip out any identifying factors to comply with privacy rules and send data to marketing platforms so their algorithms can be optimised
    • check the data quality before sending it to the platforms
    • add extra details about the lead from your CRM, and send this to GA4 for reporting, e.g. this lead is in the CRM with a quality rating (information you may not want to be seen by the end user, for which any client-side data is available to)
    • send it to any marketing or analytics platform that offers an API
    • send it directly into a database table for real-time reporting.
Diagram 2
Diagram 1

Implementing server-side tag management

Server-side tagging, as its name suggests, lives on a server, though it does not have to be the same server your website lives on. There are many options out there, but if you are using Google Tag Manager, we highly recommend using Server-side Google Tag Manager to implement your server-side tagging.

Server-side Google Tag Manager 

Server-side Google Tag Manager (GTM) provides a familiar interface for managing your tags in a new, server-based environment. It simplifies setting up a server container and lets you use pre-built templates for common vendors, such as Google Analytics and Meta. It has a one-click setup in Google Cloud (note that this sets up the servers in the US and will incur Google Cloud charges), or it can be easily set up on your own servers.

Your roadmap to server-side tag management

Luminary provides a clear roadmap for implementing server-side tagging:

  1. Decide which platform is going to do the server-side tagging. We recommend Google Tag Manager if you already use it for your tracking.
  2. Decide where the server is going to live: will it be the same server as your website, or will you use Google Cloud, which offers an easy process for setting it up and load balancing across countries if needed.
  3. Understand the costs involved with your setup; no server-side tagging is free because you always have to pay for the server.
  4. Create a subdomain on your website to use as the tracking server domain. This allows for first-party cookies.
  5. Create a clear event-naming taxonomy for GA4 that will be used as much as possible across all platforms, so that every event on every platform means the same thing. Document when names need to be different (such as viewContent for Meta instead of view_item in GA4).
  6. Document what transformations need to happen to any data source. Does the IP address need to be removed for Meta tags? Are we adding a profit margin to purchases for Google Ads?
  7. Set up the server and send data to a test GA4 property for an agreed period to check data quality.
  8. Once we are happy with the data quality, move all tracking to the GTM server side.
  9. Monitor any difference in site speed and data quality.

Embracing the future of digital measurement

Though this may seem like adding an extra step and extra costs to something that works fine as it is, the current benefits will be seen, and you will be setting yourself up for the future of tracking. In the future, you will need to have control of what data you are sending and to whom to ensure data transparency. You may also need to enrich your data from other platforms to ensure you stay ahead of your marketing spend. The more that algorithms are taking over jobs, the more we need to make sure they are being fed the best quality data to make the right decisions.

Main image: Tara Winstead on Pexels

Sarah Crooke
Sarah Crooke

18 December 2025

6 minute read

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