GTM Custom HTML Tags Explained

A Custom HTML tag in Google Tag Manager contains hand-written HTML/JavaScript. It’s the catch-all used to deploy any pixel or script that doesn’t have an official GTM template.

Why it’s used

Plenty of vendors — or bespoke scripts — have no gallery template, so they’re pasted into a Custom HTML tag. That flexibility is powerful but makes audits harder, because the tag’s purpose isn’t labelled.

Identifying them

Tag Explorer reads the code inside each Custom HTML tag and identifies known pixels (Meta, TikTok, StackAdapt and more) automatically. For anything it can’t name, use the Details button to see the raw code and work out what it is.

Best practice

Prefer an official template over Custom HTML where one exists — templates are sandboxed, safer and self-documenting.

How to check yours is working

Run your site through our free Tag Explorer tool — it shows every tag on the page, nested under its GTM container, with the tracking IDs. To confirm a tag actually fires, use GTM’s Preview mode or your browser’s DevTools Network tab.

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Part of the Shipwreck Studio Tag Guide. Scan any page with Tag Explorer to see its full tag tree and spot duplicates.