At a glance the headline numbers for Tag managers on page
Tag managers present on the page.
87.2% of sites load Google Tag Manager.
The tag managers on page mix who uses what, and how fast each group loads
Tag managers on page. On the fleet: 87.2% google tag manager, 8.7% matomo tag manager, 1.6% tealium iq. 100.0% of sites use at least one google_tag_manager.
Why this matters for the Core Web Vitals, and where to start fixing it
A tag manager is remote code execution for the marketing team. It loads first, then injects whatever the container holds: more scripts, more pixels, more vendors. None of it passes through your build or your code review, and all of it runs on your visitor's main thread.
The manager itself is not the cost. The contents are, and containers only ever grow. Audit the container like a dependency list: every tag has an owner, a purpose and an expiry date, or it goes.
Chrome field data from 189,915 sites, representing millions of real page loads. How we measured.