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Cross-domain tracking

Cross-domain tracking is a Google Analytics setup that keeps one visitor and one session as a shopper moves between your own domains, such as shop and checkout.

How it works

Google Analytics 4 (GA4) recognises a visitor and a session by first-party cookies, and a cookie belongs to one domain. Without cross-domain tracking, each domain sets its own IDs, so one shopper counts as two users and two sessions. With it, the Google tag adds a _gl parameter to links and forms leading to your other listed domains, so the next domain keeps the same IDs.

For a store, this matters when the checkout runs on a different root domain. Without the setup, the order lands in a new checkout session that has lost the ad click and starts as a referral from your own catalogue. Every domain needs the same Google tag ID, and a redirect that drops _gl breaks the chain. Our guide to GCLID and auto-tagging in GA4 covers other reasons an order loses its ad click.

Where you see it

  • Google Analytics: Admin → Data streams → web stream → Configure tag settings → Configure your domains.
  • Address bar: after a click to the other domain, the URL carries _gl=…. If not, check the domain list and redirects.

Example

Example store, not client data.

The tableware shop shows its catalogue on tableware.example and takes payment on tableware-checkout.example, both with the same Google tag. A shopper clicks a Shopping ad and pays 600 for a dinner set. Without the setup, GA4 counts two users and two sessions, and the 600 purchase lands in a session referred by tableware.example. With both domains listed, GA4 counts one user and one session, and the 600 stays with the ad click.

Not to be confused with

  • Auto-tagging — adds the click ID (GCLID) to the landing URL so GA4 knows the visit came from an ad. Cross-domain tracking carries the visitor on to your next domain.
  • UTM parameters — labels for the source of a visit. They do not carry a visitor’s identity between domains.

Right and wrong readings

  • Wrong: “Cross-domain tracking fixes orders credited to the payment processor.” Right: the setup needs your tag on every domain, and a third-party payment processor’s site doesn’t carry it. For that case, Google offers a list of unwanted referrals.

Sources