Google Tag Manager (GTM) is one of Google's best products - second only to its ubiquitous and feature-rich Google Analytics product. GTM, as its name implies, is a tag manager that's used to embed JavaScript, HTML, and/or CSS code into websites. Such code can include, but is not limited to, analytics scripts like Google Analytics, tracking beacons from online advertisers, and proprietary content from websites themselves. There's no denying that GTM is a powerful tool; one that represents a major shift forward from the bad old days of self-hosted, spaghetti-code. But like most technology, if it's not used correctly, GTM could end up causing more problems for a website than it solves. Problems having to do with slow performance, mostly; but also tag misfires, data corruption, and quota limitations. In this article, we'll be discussing solutions to such problems by exploring the five (5) common mistakes that websites make when setting up GTM. Mistake #1: Not