Google Tag Manager

A container you deploy once, then use to add, edit, and version marketing tags without touching site code again.

GTM ships a container snippet; inside it you define tags, the triggers that fire them, and the variables they read, then publish versions independently of engineering releases. It earns its place the moment you run more than a couple of vendors or need consent mode enforced in one location. The common confusion is thinking GTM measures anything itself; it only deploys other people's tags, and a broken trigger collects nothing.