Google Tag Manager: Lookup Table Variable

The Lookup Table variable in Google Tag Manager allows you to read the value of an input and, if this value matches certain requirements, it will return some output.

There are several situations where this variable can help us: rename a web page, rename the Source dimension for a social (Instagram, Facebook LinkedIn etc.) and so on.

In this post I’ll show you how to use this variable, when we have two or more identical websites that have their own Google Analytics Property:

In such a situation, we can:

1. Use a single Google Tag Manager container and triple all tags for each property (1, 2 and 3);
2. Create three Google Tag Manager containers;
3. Use a single container, without tripling the tags, and use the Lookup table Variable

Option number 3. is the best because it saves a lot of time and, above all, reduces the errors that can result from duplication.

Contents of the article:
- Create the Lookup Table Variable for Multiple Websites
- Insert the Variable in the Tag of GA4
- Insert the Variable in the GA Universal Analytics Tag

Create the Lookup Table Variable for Multiple Websites

At this point we can create the variable, going to Variables> New (User-Defined Variables):

Then we select the Lookup Table Variable:

At this point we have to:

1. select the Input Variable: we have to choose the parameter (eg: Page Hostname) on which to base the choice whether to send the information to Property 1, 2 or 3 of Google Analytics;
2. select the number of Outputs: indicate the Property ID or the Google Analytics 4 Measurement ID for each website;
3. select the type of Input: indicate the value according to point 1.: if I choose the Page Hostname I must indicate the domain of the website:

Important: when we use this variable, we have to know that the value typed in point 3. is considered as an “exact match”. This means that, if I have a sub-domain (eg: blog.example.com), in the input I have to write the sub-domain for it, to be read correctly. If you entered example.com, the blog.example.com subdomain would not be read.

Another important thing to remember: if I select {{Page Hostname}} in point 1. it is not necessary to write ‘https’ in point 3. also. You can see it simply by activating the GTM Preview to observe which is the value that is collected, as in the example below:

Insert the Variable in the Tag of GA4

Once we have created the Lookup Table variable, we need to modify the Google Analytics 4 configuration tag, so that information on user interactions on the website is dynamically sent to the different Properties of each website.

We enter the GA4 tag that interests us and click on the brick 1).

A list will appear, so we select the Lookup variable we created earlier and insert it.

Each tag that refers to Google Analytics 4 must have this variable.

In this way:

• the user’s action on the website sends an event to the data layer
• the event is read by GTM and activates the tag
• the information is sent to the various Properties created in GA4, based on the value of the {{Page Hostname}} variable

Let’s save the tag.

Insert the Variable in the GA Universal Analytics Tag

The same work can also be done if we were working on the Universal Analytics Property.

We will need to create the Lookup variable, as in the steps above.

The only thing that will change will be the Property ID, i.e. the tracking ID to be entered, which we find in the Property under Admin> Property Settings

This ID will be copied and output to the Lookup Table variable:

Next, we’ll need to go inside the tag that sends the information to Universal Analytics and:

1. Click on Enable overriding settings in this tag
2. Click on the brick to select the Lookup Table variable created earlier

Then save, test everything and publish the new changes in the container.

Good analysis!

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