Lesson 2 of 5

Audit What'S Already There

Before changing anything, inventory every tag currently firing. Skipping this step is how migrations lose data, you can't replace a tag you didn't know existed.

How to find them

Tag Assistant / a tag scanner: load key pages and list what fires.
DevTools Network: filter for collect, facebook, googleads, etc., to see real outbound hits.
Search the source: grep the codebase/theme for gtag, fbq, analytics.js, hard-coded IDs.
Ask the team: which platforms do marketing actually use? Orphaned tags are common.

Build a tag inventory

Tag            | ID          | Where it lives        | Fires on        | Keep?
GA4            | G-ABC123    | <head> hard-coded     | all pages       | move to GTM
Meta Pixel     | 9988...     | footer.php            | all + Purchase  | move to GTM
Old UA         | UA-12345    | <head>                | all pages       | remove (dead)
Google Ads     | AW-555      | thankyou.html inline  | conversion      | move to GTM

Key takeaway

Produce a written inventory, every tag, its id, where it lives, what it fires on, and whether to keep it. The audit is the migration plan.