What is Cross-Domain Tracking?
A configuration that allows GA4 to pass identifiers across different domains, ensuring a single user journey isn't split into two separate sessions.
When a user clicks a link from your main website (shop.com) to a third-party checkout or portal (secure-checkout.com), their browser considers them a completely new visitor because cookies cannot be read across different domains.
Cross-domain tracking solves this by appending a special URL parameter (the _gl parameter) to the destination link. When the user lands on the second domain, GA4 reads that parameter and stitches the two sessions together.
The symptoms of broken cross-domain tracking:
If you haven't set this up correctly, you will experience:
- Inflated User/Session counts: Because every crossing is counted as a new user.
- Self-Referrals: Your main domain will show up in your reports as the referring traffic source for the conversions that happen on the second domain.
- Broken Attribution: The original traffic source (e.g., a Facebook Ad) gets lost, and the conversion is attributed to "Referral".
A GA4 audit tool like NiceLookingData checks exactly for these domain mismatches and missing _gl parameters.
Does your GA4 have Cross-Domain Tracking issues?
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