Google Tag Manager.

Google Tag Manager (GTM) is a free tag management system from Google that allows marketing and analytics tags to be managed centrally on a website — without modifying the source code for every change. Tags are small code snippets from tools like Google Analytics 4, Google Ads Conversion Tracking, Meta Pixel, LinkedIn Insight Tag, and others. Without GTM, a developer would have to embed each tag individually in the HTML code — with GTM, this is done through a visual user interface.

GTM works with three concepts: Tags (what should be measured/executed? e.g., GA4 pageview), Triggers (when should the tag fire? e.g., on page load, button click, form submission), and Variables (what data should be passed? e.g., page name, click URL, form value). This combination enables complex tracking without code changes.

In 2026, Server-Side Tagging is the most important trend in tag management: Instead of executing tags in the user's browser (client-side), data is routed through a dedicated server container. Benefits: less data loss from ad blockers (20–30% more data), better website performance (less JavaScript in the browser), better data privacy compliance, and more accurate conversion tracking. DLM Digital uses Server-Side GTM as the standard for client projects.