What is Google Tag Manager and what is it used for? Complete guide with form tracking

Here’s what you’ll find in this guide:

• What Google Tag Manager is and how it works behind the scenes
• How it is used in the day-to-day management of a digital marketing strategy
• Why it is important to configure it properly, even if you are not a technical company
• Step-by-step guide: how we set up conversion tracking for form submissions at VILAX

What is Google Tag Manager?

Google Tag Manager is Google’s free tag management system, which centralises the installation and activation of tracking codes on a website — Google Ads, GA4, Meta and others — from a single dashboard, without having to edit the page code every time a change is made.

The first mistake is thinking that Google Tag Manager “measures” anything by itself. It does not. GTM is the layer that determines which measurement tools are loaded, when they are triggered and what data they receive. If that layer is configured incorrectly, Google Ads or GA4 may be optimising based on incomplete or outright incorrect data.

Before GTM existed, every time a Meta pixel, a Google Ads conversion tag or Google Analytics tracking needed to be installed, a developer had to edit the website’s code. With GTM, that process is reduced to installing a single code snippet once — the container — and from that point on, everything is managed through the Tag Manager visual interface.

How does Google Tag Manager work?

GTM works with three connected components inside a container: tags send data to other platforms, triggers determine when they fire, and variables provide the dynamic values that both need.

GTM is organised around three components that work together:

Tags: these are snippets of code that send data to other platforms, such as Google Ads, GA4 or Meta. For example, a tag can notify Google Ads that a conversion has occurred.

Triggers: these are the conditions that determine when a tag fires. This could be when a specific page loads, when a button is clicked or, as we will see in the form tracking guide, when an element becomes visible on screen.

Variables: these are the dynamic values used by both tags and triggers to determine exactly which data they need to pay attention to in each case.

All of this is managed within a container, which only needs to be installed once in the website’s code. From that point on, any tracking changes are made from the GTM interface, without having to edit the source code again.

What is Google Tag Manager used for?

It is used to track conversions, centralise all website tracking in one place, give the marketing team greater autonomy from developers, and test every change before publishing it.

In the day-to-day management of a digital marketing strategy, GTM is used to:

Track conversions: form submissions, purchases, clicks on call buttons, downloads… any action you want to turn into measurable data.

Centralise tracking: instead of having Google Ads, GA4 and Meta Pixel code scattered across the website, everything is managed within a single container.

Work independently from developers: the marketing team can add, test and publish a new tag without relying on a developer’s availability.

Test before publishing: GTM’s Preview mode allows you to check that a tag fires correctly before the change goes live on the website, helping to prevent tracking errors that can be very difficult to detect later.

Why is Google Tag Manager important for your business?

It is important because advertising investment decisions depend on reliable conversion data: without GTM being properly configured, and without respecting user consent, those decisions are made using incomplete or inaccurate data.

The main reason is speed of response. Any advertising investment decision — how much to spend, on which campaign and with what budget — depends on having reliable conversion data. Without properly configured tracking, those decisions are made blindly.

With GTM, when you launch a new landing page, change a form or want to track a new action, the change can be made the same day, rather than waiting for the technical team’s next available slot. Over months of campaign activity, that makes the difference between optimising with real data and continuing to invest blindly.

There is an additional reason: measurement is becoming increasingly sensitive to browser restrictions, ad blockers, consent requirements and the loss of identifiers. One evolution of GTM is server-side tagging, where part of the tracking process is handled through server infrastructure controlled by the company. This can provide greater control over data and improve certain measurement setups, but it does not remove the need for consent or solve every form of data loss on its own.

And there is one rule worth making clear: Google Tag Manager does not replace a consent management platform. If an advertising tag requires consent, GTM must be configured to respect that consent before firing it.

How do you set up a form submission conversion in GTM?

The process has two parts: creating the conversion action in Google Ads and then creating the tag in Google Tag Manager that triggers it, using the most reliable trigger available based on how the form is built.

There are several ways to track when someone submits a form with GTM: detecting the submission event, tracking a thank-you page or using the visibility of the confirmation message. At VILAX, we use the latter option when the form does not reload the page or redirect and no more robust event is available in the dataLayer. It works well for many dynamic forms, provided that the success message has a stable selector and only appears after a successful submission.

How do you create the conversion action in Google Ads?

The conversion action defines which behaviour you want to count as a lead, how it should be recorded and whether Google Ads should use it to optimise campaigns.

1. In Google Ads, go to Goals > Conversions > Summary > Create conversion action.
2. Choose the “Conversions on a website” data source and click Save and continue.
3. In the section for grouping conversions, select “Submit lead form” and, in the tab that opens, choose “Set up manually using code”.
4. Complete the setup. Under Conversion optimisation, use “Primary action” if you want this conversion to be used for campaign optimisation. Give it a clear, identifiable name, for example “Website form submission”. Under Value, assign a value only if it reflects a real business rationale; if you know the average expected value of a lead, you can use it to guide optimisation more effectively. Under Count, for lead generation we normally recommend “One”, because it prevents multiple submissions from the same person after an ad interaction from inflating the number of opportunities. “Every” makes more sense when each repeated action generates independent value, as is usually the case with sales. Review the remaining options based on the account’s conversion window and attribution model, then click Done.
5. In the “Create and measure conversions” section, you will see the manual conversion you created. Click Save and continue.
6. In the “Finish setting up your conversions” window, click Use Google Tag Manager. Copy the Conversion ID and Conversion Label shown here — you will need them in the next step.

How do you create the conversion tag in Google Tag Manager?

In Google Tag Manager, you need to create the Google Ads conversion tag and assign it a trigger that only fires when the form has been submitted successfully.

1. In your Tag Manager account, go to the Tags tab and click New. At VILAX, we recommend giving it the same name as the conversion in Google Ads so that it is easy to identify.
2. In the tag configuration, select Google Ads > Google Ads Conversion Tracking. Enter the Conversion ID and Conversion Label you copied from Google Ads.
3. In the Triggering section, click the “+” button to create a new trigger and select the Element Visibility option.
4. In the trigger configuration, under Selection Method, choose CSS Selector.
5. To obtain the selector, go to the page where the conversion takes place and submit the form yourself. When the success message appears, inspect the element. Whenever possible, use a stable ID or CSS class that is specific to the confirmation message. The browser’s Copy > Copy selector option can be used as a starting point, but some automatically generated selectors are too fragile and may stop working if the page structure changes.
6. Make sure these settings are retained: under “When to fire this trigger”, select “Once per page”; under Advanced settings, set the minimum percent visible to 50; and enable the “Observe DOM changes” option, which is necessary because the confirmation message usually appears dynamically without reloading the page.
7. Save the trigger and the tag, but do not publish yet. First, enter GTM’s Preview mode, connect the URL where the form is located and submit a test form. In Tag Assistant, check that the conversion tag fires only once after a successful submission and that it does not fire when the page loads or when a validation error occurs.
8. Once the test is successful, publish the container from “Submit”. Then make a second real submission and also check the conversion status in Google Ads. The Google Ads interface may take some time to reflect or update the measurement status, so an implementation should not be considered unsuccessful simply because it does not appear immediately.

Important: also review how the Google tag and conversion linking are implemented. Google states that if the container already loads a Google tag on all pages, there is no need to add a separate Conversion Linker tag. In setups where that global Google tag is not present, the Conversion Linker helps preserve ad click information and attribute the conversion correctly.

Reliable measurement is not a one-off task: it is the system that Google Ads, GA4 and other tools rely on to make decisions. If a tag, trigger or consent setup fails, the final data will fail too. If you want to check whether your conversions are being tracked correctly or implement Google Tag Manager from scratch, get in touch with us.