It is a requirement that developers install the chrome plugin to validate the GTM code:

https://chrome.google.com/webstore/detail/tag-assistant-by-google/kejbdjndbnbjgmefkgdddjlbokphdefk?hl=en

It is recommended to set chrome plugin to “Detailed” mode, rather than “Basic” mode:

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Here is an example of the Chrome validator in action:image088

 

Clicking on the “not working” shows details:

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Tip: JSON validator is really good for checking the dataLayer

http://jsonlint.com/ for example

{

“variableName”: “textValue”,

“variableName”: “textValue”

}

Note: jsonlint.com does not like HTML comments, and single-quotes need to be changed to double-quotes in order to validate.

 

Also JSON formatter for chrome can also be used to make JSON easier to read.

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