What is a Google Tag Manager (GTM) Injector?

Tag Manager Injector is a chrome extension which helps you to preview a GTM container on your site (or your client’s) without needing to add any JavaScript to your pages. It means you have much more time to test your GTM configuration in advance and you do not have to wait for a developer to add the code.

You can download the extension here. Also, DataLayer Inspector has the same functionality. Read the full guide how to use Tag Manager Injector. P.S. The plugin is now paid and if you are looking for alternatives, here they are.