Google Tag Manager Tutorial Part #3: Tag Migration
What is tag migration?
Tag migration is the process of moving your existing tracking to GTM.
If you start publishing new tags in GTM before you migrate your old tacking tags, you'll double up your tracking.
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For example, let's say you have the analytics.js code snippet installed on your site. But then you publish a Google Analytics tracking tag in GTM. If both of these tags are sending data to the same Google Analytics property, all your data will be double counted.
So it's imperative to remove your existing tracking, before you install new tags in GTM.
Tag Migration checklist
The migration process works like this:
-Categorize and record all the existing tracking tags that are running on your website
-Recreate those tracking tags in GTM
-Use preview mode to test your new tags
-Remove all your current tracking
-Publish your GTM container with your new tracking tags
How can you make sure you don't have any gaps in tracking while you're working on tag migration?
If you have a lot of tracking tags in place, it may take you a while to remove your current tracking scripts.
But you want to make sure that you are not double-tagging your pages. You don't want to fire your new GTM tags until the old scripts have been removed.
If you aren't careful, the migration process could cause a gap in your tracking, so you need to plan this migration carefully. The gap would be in the time between when your old tracking scripts are removed and when your new GTM container goes live.
GTM migration trigger
There is a GTM technique you can use to eliminate tracking gaps during tag migration. This technique involves creating a suppression trigger. The suppression trigger tells GTM not to fire your new tracking tags if the old tracking code can be found on your site.
The second the old tracking is removed, the suppression trigger will stop firing, and your new tracking tags will start recording data. This trigger will prevent double tracking, and it will eliminate gaps in your reporting.
I am thinking about writing a blog post on this technique for migrating tags, but only if you're interested. Leave a comment if you'd like to see a detailed blog post.
Tag migration can feel like a complicated process. Leave a comment on this post if you would like me to build a more complete migration checklist or a technical guide to migrating tags. If there are enough requests for full tag migration checklist, we'll create one and share it with you.