In this guide
- Cross-domain tracking passes a client ID from one domain to the next, so GA4 sees one session.
- In GA4 you list your domains in the data stream settings, and the tag adds a
_gllinker parameter to links between them. - One server container can serve several of your sites. With Open Tracked that is the Multi-Domains power-up on the Business plan and above.
Many businesses run more than one domain: a shop and a separate checkout, a brand site and a store, several country sites. Browsers keep cookies separate for each domain. If you do nothing, a visitor who moves from the first to the second looks like a new person, the session breaks and the sale is credited to "referral" from your own site. This page explains how to fix that for analytics and ads, and how a server container handles more than one domain. See also server-side GTM with multiple domains and cross-domain tracking with cookie restore.
The problem
| Without cross-domain tracking | With it |
|---|---|
| New session on the second domain | One session across both |
| Your own site appears as a referrer | The original source is kept |
| The purchase is credited to "referral" | The purchase is credited to the real channel |
| Two client IDs for one person | One client ID |
Works with your stack
Grab a logo and throw it. These are the tools Open Tracked already talks to.
GA4 cross-domain measurement
Open the web data stream settings
In GA4 Admin, Data streams, your web stream, Configure tag settings, Configure your domains.
Add every domain involved
Use match conditions such as "contains" for each domain.
Check the self-referral list
Add the domains to the referral exclusion list if needed.
Test
Click a link between the domains and check that the address gains a _gl parameter and that the client ID is the same on both.
The _gl parameter carries the client ID across the link. Forms that post to another domain, redirects and payment pages can drop it, so test every route that crosses domains.
One server container, several domains
A server container can receive events from several sites, each on its own tagging subdomain, for example data.shop-a.com and data.shop-b.com, both pointing to the same container. With Open Tracked, you turn on the Multi-Domains power-up (Business plan and above), add each site's own subdomain in Settings, Domains, point its DNS record to us and press Verify. All the domains reach the same server container. Use the hostname in triggers and variables to treat each site differently, for example to send each to its own GA4 property.
Orders from your store, back to the ad that earned them
Your store sends the order once. Open Tracked passes it on to each ad platform, cleaned and deduplicated.
When to use one container and when several
| Situation | Suggestion |
|---|---|
| Several sites of one business with the same tags | One container, Multi-Domains |
| Sites with different tag sets or teams | Separate containers |
| Different clients | Always separate containers |
Cookies and consent
- Cookies are per domain. Each site sets its own first-party cookies from its own tagging subdomain.
- Consent given on one domain does not carry to another unless you share it. Plan how consent is recorded across sites.
- Do not share personal data between domains without a lawful basis and a clear notice.
Common problems
_gl.Check your tracking in one pass
This is an example. Run the check on your own site to see where yours stands.
Frequently asked questions
What is cross-domain tracking?
Passing the visitor's identifier from one domain to another so analytics sees one session.
How do I set it up in GA4?
List your domains in the data stream settings under Configure your domains and test that links gain a _gl parameter.
Can one server container handle several domains?
Yes. With Open Tracked, the Multi-Domains power-up on the Business plan and above lets you add a tagging subdomain for each site.
Why do I see my own site as a referrer?
The domain is not configured for cross-domain tracking or the linker parameter is lost.
Do I need a separate container for each site?
Not for sites of one business with the same tags. Different clients need separate containers.
Do I need spreadsheets to read my results?
No. Once tracking is live, the Open Tracked analytics shows spend, revenue, ROAS and profit, and you can ask Ari, the built-in AI assistant, questions about your own numbers in plain words. Ari's allowance depends on your analytics plan.
Is Open Tracked different from Open Track or Open Space Track?
No. Open Tracked is the official name of our server-side tracking platform, and the website is opentracked.io. Many people search for it as Open Track, OpenTrack or Open Space Track. All of them lead to the same product: server-side Google Tag Manager hosting, first-party analytics and a CRM pipeline.
Fix your tracking at the source
Open Tracked hosts your server-side Tag Manager, keeps first-party cookies alive and shows what each ad is really worth.
The Open Tracked team
We build Open Tracked: server-side tracking hosting, analytics and the tools around them, for stores that spend on ads. Questions about this guide, or an idea for the next one?
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