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GA4 - Cross-Domain Tracking

Last updated on Mar 24, 20263 min read
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In short​

Many companies have several websites that they want to track across domains. For example, products are advertised on a separate website, while the checkout takes place on another website.

Cross-domain tracking measures user sessions across multiple domains and provides a complete picture of the user journey. It is particularly indispensable for such scenarios, but often poses challenges.

This guide shows how cross-domain tracking can be set up easily and effectively in GA4.

What is cross-domain tracking?​

Cross-domain tracking, combines user sessions across different domains into a single one. Without this function, users who switch from one domain to another are counted as separate sessions and users. In addition, conversion events (key events) cannot be assigned to a user across multiple domains.

Cross-domain tracking is indispensable for companies with separate checkout or booking platforms or for groups with several brands. It provides a clear overview of traffic, engagement and web performance.

It is particularly important for the evaluation of cross-domain A/B tests.

How to set up cross-domain tracking for GA4​

Installation of cross-domain tracking in GA4​

Setting up cross-domain tracking in GA4 is much easier compared to Universal Analytics, as the entire configuration is done within GA4. Here is a detailed guide on how to set up cross-domain tracking in just a few steps:

Step 1: Make sure that GA4 is installed on both websites​

  • Both websites must use the same GA4 property.
  • Implement the GA4 tracking code either directly in the page source code (via gtag.js) or via the Google Tag Manager (GTM).
  • Make sure that the GA4 code is correctly integrated on all pages and that the data is sent to the same property.

Step 2: Configure domains for cross-domain tracking​

  1. Log in to your GA4 account and go to Admin.
  2. Choose from Data collection settings the point Data streams.
  3. Select the corresponding data stream (e.g. "Website stream").
GA4 admin under „Data streams“ with the web stream of the site highlighted
  1. Scroll down to Configure tag settings and click on it.
Google tag section of the data stream with the entry „Configure tag settings“ highlighted
  1. Go to Configure your domains.
Tag settings with the highlighted entry „Configure your domains – Specify a list of domains for cross-domain measurement“
  1. Add the domains you want to track (e.g. domain1.com and domain2.com).
  • Enter the URLs without a prefix such as https:// .
  • GA4 will automatically treat these domains as belonging together and link the data.
GA4 „Cross-domain Linking Configuration“ with two conditions of type „Contains“, one per domain taking part in the test

Step 3: Ensure URL parameters for user tracking​

  • GA4 uses the URL parameter _glto transfer information such as client ID and campaign data when switching between domains.
  • This parameter is added automatically if cross-domain tracking is set up correctly.
  • Check whether the _gl-parameter appears in the URL when a user navigates between the two domains.

Step 4: Test and check​

  • Navigate between the two domains and check in GA4:
    • Are sessions and users tracked consistently across both domains?
    • Is the traffic correctly assigned and not displayed as "referral traffic" between the two domains?
  • The navigation between the domains should appear seamless in the reports.

Advantages of cross-domain tracking with GA4​

With cross-domain tracking in GA4 you can:

  • Trace the user path across multiple domains.
  • Correctly aggregate sessions, conversions and events.
  • Ensure that Analytics reports are not distorted by incorrect referrals or duplicate sessions.
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