Detailed definition
Classic GTM runs in the browser (client-side); with iOS 14.5, the death of third-party cookies and ad blockers, data loss now reaches 30-40%. With server-side GTM the tags run on your own server (Google Cloud Run, Stape), so the data is passed to Meta and Google as first-party. The set-up is complex, but the effect on data quality is significant.
Examples
- A beauty brand raised its Meta conversion match rate to 85% with server-side GTM (previously 55%).