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Why GTM Preview Mode might not work on your site

I was trying to run a Preview of Google Tag Manager for a site I was working on, but for some reason it simply wasn’t showing. Turning to the Console as always when something unexpected happens (or doesn’t happen), I saw an error message about my ‘Content Security Policy directive’ being violated.

Basically, a CSP is a directive that says what content is allowed on a site. For example, it might say that external scripts aren’t allowed. And in my case, it wasn’t allowing the debug mode of GTM to be delivered from the domain

To get round this (if you don’t want to change your CSP) use a handy Chrome extension called Disable Content-Security Policy.

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