What is Google Tag Manager?
GTM is Google's free tag management system. It lets you add and change tracking codes from one interface, without editing the site's source code every time.
The core concepts
- Tags are code snippets that send data to services such as GA4, Meta Pixel or the LinkedIn Insight Tag.
- Triggers decide when a tag fires: on page load, a click, a form submission or a custom event.
- Variables are dynamic values such as the URL, the clicked button text or a product name.
- The dataLayer is a JavaScript array on your site that passes information from the website to GTM.
Container structure and versioning
GTM has built-in version control. Every publish creates a new version, changes can be previewed before they go live, and a rollback takes one click.
GTM and Consent Mode v2
Consent Mode v2 is set up with an initialization trigger that runs before any other tag. Your consent management platform passes the visitor's choice to GTM, which then allows or blocks tags. For EU traffic in 2026 this setup is always required.
Common GTM mistakes
- Duplicate GA4 tags, added both in GTM and directly in the code, which double-count pageviews.
- All Pages triggers without consent conditions.
- No trigger on form submissions, so the most common conversion goes untracked.
- Missing dataLayer on e-commerce sites, which makes product tracking impossible.
Frequently asked questions
Is GTM free?
Yes, the standard version is free. GTM 360 exists for enterprises.
Does GTM slow down my site?
The GTM script is small and loads asynchronously. The tags you add are what affect speed, so a clean configuration keeps the impact minimal.
Can anyone use it?
Basic tags are easy to learn. Consent Mode, dataLayer integration and advanced setups call for technical skill or a specialist.
Web container or server container?
The web container runs in the visitor's browser. The server container (sGTM) runs on your server and forwards data from there. It is required for server-side tracking.