Google Tag Manager (GTM) is a free tool that lets you add and manage tracking tags on your website without editing code directly. It is widely used and very useful — but it can become a performance problem when not managed properly.  GTM performance issues show up as increased page load time, poor Largest Contentful Paint (LCP), high Total Blocking Time (TBT), and lower Google PageSpeed Insights scores. 

Common causes:

too many tags firing on every page, heavy third-party scripts loaded through GTM, tags firing at document start (blocking rendering), outdated or duplicate tags that were never removed, and complex trigger conditions that slow GTM’s own processing. 

How to fix GTM performance issues:

Open GTM Preview mode and see exactly which tags fire on which pages. Remove unused tags — even inactive ones add to container file size. Set triggers correctly so tags only fire when and where needed. Use the Timeline in GTM Preview to spot slow-loading tags. Move to server-side GTM to offload heavy tracking from the browser entirely. 

Seers.ai works with server-side GTM to manage consent and tag firing in one place — improving both privacy compliance and website performance without complicated custom code.