Google Tag Manager explained: the basics for SMEs

Google Tag Manager is the free place where you manage your website's measurement and advertising code, such as the Google tag and the Meta pixel ^{[1], [2]}. You place two code snippets once, then you work in the web interface. Create the account in your company's name, load your cookie banner first and test every change before you publish.

Even if a Google Analytics agency or your web developer sets it up, it pays to know the basics. Tag Manager decides which data leaves your website, to whom, and whether that only happens after consent. It doesn't measure or report anything itself: GA4 does that.

Do you need Tag Manager?

Not always. For the standard measurement of page views, clicks and scrolls, the Google tag is enough, but if you want more control, Google recommends Google Tag Manager ^[3]. The Google tag also only sends to Google, while Tag Manager sends to other parties as well ^[3].

Who should be the owner?

Your own company. Google recommends that your company creates the account and adds an agency as a user, that someone from your own organisation manages it, and that there is at least one additional administrator ^[5]. If your only administrator drops out, you can lose access to your tags ^{[5], [6]}.

A workable split for an SME: two people from your company are administrators of the account, and your agency gets publish rights on the container. Between read and publish there are two more levels: edit (make changes, but not create versions or publish) and approve (also create versions, but not publish) ^[6].

Every publication saves a version, which you can set as the latest version again if something goes wrong ^[7]. Export your container as a JSON file whenever you change agency or web developer ^[8]. Tag Manager then belongs on the handover list, next to your advertising accounts: see How to transfer a Google Ads account or switch agencies.

A fixed naming convention makes your container readable for whoever comes after you, for example destination, type and action: GA4 - event - generate_lead for the tag and CE - generate_lead for the trigger.

Tags, triggers, variables and the data layer

A tag is code that sends data to a system such as GA4. A trigger listens for events, such as a click or a page load, and makes tags fire. A variable is a named placeholder for a value that changes, such as a price ^[9].

Together they form a container: all the tags, triggers and variables for one website ^[1]. Google recommends one container per domain ^[5]. A bilingual site with /nl/ and /fr/ on one domain therefore needs only one container.

The data layer is the object your website uses to pass information to Tag Manager ^[10]. Google prefers it to values taken from the page's markup, because a code change is then less likely to cost you data ^[9]. An example: your site runs this code as soon as a quote form has actually been sent.

window.dataLayer = window.dataLayer || [];
window.dataLayer.push({
  event: 'generate_lead',
  form_name: 'offerte'
});

A trigger of the Custom Event type on generate_lead then fires the GA4 tag and the Google Ads conversion tag, and a failed submission doesn't count. Why that moment makes the difference is explained in GA4 key events and conversions: the difference explained.

Put this in the brief for your web developer:

• which events the site passes on, with exact names and parameters, the same on every page ^[10];
• that the data layer comes before the container code and is then only added to with dataLayer.push(), never overwritten ^[10];
• when each event fires: after a successful submission or payment, not on the click on a button.

You set consent per tag

In Belgium you need prior consent for analytics and advertising tracking, including pixels, device fingerprinting and local storage ^[11]. A pixel via Tag Manager is covered just as much as a pixel in the code. Tag Manager has four tools for this ^[4]:

• The Consent Initialization trigger for your cookie banner. It always fires before all other tags, including Initialization triggers.
• Built-in consent checks in Google's tags, such as those of GA4 and Google Ads.
• Require additional consent for tag to fire for third-party tags, such as the Meta pixel. The tag only fires if all the specified consent types are set to granted.
• The Consent Overview, which you turn on in the container settings. It shows which tags don't have a consent setting yet.

Don't set consent with a Custom HTML tag, but with Tag Manager's consent APIs, for example via your banner provider's template in the Community Template Gallery ^{[4], [10]}. Whether to choose basic or advanced Consent Mode is covered in Consent Mode v2 in practice: basic or advanced?.

Getting started in six steps

1. Create the account in your company's name, at tagmanager.google.com: one account per organisation, one container per website ^{[1], [12]}.
2. Place the two code snippets: the first as high as possible in the <head>, the second directly after the opening <body> tag ^[13].
3. Load your cookie banner first, on the Consent Initialization - All Pages trigger ^[4].
4. Add the Google tag on the Initialization - All Pages trigger. On another trigger, GA4 can show sessions without source and medium, as (not set) or Unassigned ^[14].
5. Test in preview mode. Tag Assistant shows which tags fired and in what order; your visitors see none of it ^[15].
6. Publish with a version name that says what changed ^[7].

For Google Ads and GA4, use the built-in tag templates, not Custom HTML with gtag.js code ^[10]. Templates from the Community Template Gallery come from external developers: check the permissions they ask for ^[16]. And never load GA4 twice, via your theme or a plugin as well as via Tag Manager, because then every page view counts twice.

Not sure your container is right? The free tracking audit checks which tags fire, whether they follow your visitors' consent and whether your conversions count once. Read access to your container is enough.