Google Tag Manager setup and consulting: measurement built on an event plan, consent-aware and managed by version.

We wrote this guide for marketing and ecommerce teams who want to set up Google Tag Manager on their site, or bring order to an existing container. The guide looks for answers to three questions: which tag measures what, is the cookie choice respected, and who makes the changes? The rules we describe are based on Google’s Tag Manager Help Center, the Tag Platform developer documentation and the Google Analytics documentation; we verified product names and settings against the source as of September 2026. Our own field observations are marked separately under the heading “Expert note”.

We run tag management in three layers: container structure and permissions, the event plan and dataLayer, and consent and pre-release testing. This page covers the tag layer that carries data to GA4 and ad platforms.

What is Google Tag Manager (GTM), and what is a tag manager for?

Short answer: Google Tag Manager (GTM) is Google’s tag management system, which lets you set up and manage the measurement and marketing tags on your site without changing the site’s code every time.¹ During setup, two code snippets are added to every page of the site; after that, most tag work is done from the Tag Manager interface without touching the code.¹ The whole set of tags, triggers, variables and related settings installed on a site is called a container.¹

A container can replace all the Google Ads, Google Analytics, Floodlight and third-party tags added to the code by hand.¹ Moving all tags at once is recommended but not required; migrated tags work alongside tags managed outside Tag Manager.¹ This flexibility can also lead to the same tag running from both the code and the container and counting events twice; during migration, we remove each tag’s copy in the code the moment its counterpart in the container goes live. markention.com’s own measurement also runs on GA4, Google Tag Manager and Microsoft Clarity, set up the way this guide describes.

How do tags, triggers and variables work together?

A tag sends data to a platform, a trigger decides when that happens, and a variable carries the value of that moment to both. In Tag Manager, tags fire in response to events: a trigger listens on the page for events such as a form submission, a button click or a page view, and tells the tag to fire when the event is detected.² Every tag must have at least one trigger in order to fire.² Variables, meanwhile, are used to simplify and automate tag configuration.¹

The key setting of the trio is the trigger filter. A new trigger fires on all events of its type by default; to narrow it down, you add filters, each made up of a variable, an operator and a value.² In Google’s example, a “Page URL contains /products/” filter added to a page view trigger fires the tag only on product pages.²

How is Google Tag Manager set up?

Setup consists of three jobs: opening an account in the company’s name and a container for the site, adding the container code to every page, and defining the dataLayer before that code. The dataLayer is defined as high in the source code as possible, above the container code, with the line “window.dataLayer = window.dataLayer || [];”; values Tag Manager needs to see while the page loads are also sent before the container code.³ After setup, we check that the code loads once on every page and doesn’t clash with old tags.

Tag Manager access can only be granted to Google accounts.¹¹ In an account with a single administrator, access can be lost when that person changes roles; that’s why Google recommends having at least two active administrators, and having the Google accounts used for access managed by someone inside the organization rather than an outside agency or consultant.¹¹ So we open the Tag Manager account in your name, leave administrator rights with you, and do the work with permissions granted at container level.

What is the dataLayer, and how are events sent?

The dataLayer is the object Google Tag Manager and gtag.js use to pass information to tags; the site writes an action and that action’s values to this object, and triggers are built on those values.³ An event is sent in the form “dataLayer.push({‘event’: ‘event_name’})”; the event name is a string describing the action, such as “login”, “purchase” or “search”.³ Several variables can be sent with the event in the same call; a new value sent under the same name overwrites the old one.³

Tag Manager processes dataLayer messages one at a time, in the order they arrive; if a message is an event, the tags whose conditions are met fire before moving on to the next message.³ A push or gtag() call made from on-page code, a custom template or a custom HTML tag is processed after the messages already in the queue; so an updated value may not be ready for the next event.³ The recommended solution is to send the value with an event name and listen for it with a custom event trigger.³ In our event plan every value goes with its own event; the other rules we follow during setup come from the same document:³

• Don’t overwrite: the assignment “dataLayer = […]” wipes existing values in the array; it’s defined once, and everything after is added with push.
• Case: the object’s name is “dataLayer”; a push written as “datalayer” doesn’t work.
• Consistent names: the same concept is sent with the same variable name on every page; otherwise tags won’t fire on some pages.
• Page lifetime: dataLayer variables live only while the visitor is on that page; a value needed across pages is sent again on each page.

How is the event plan built with GA4 recommended events?

The event plan is built by choosing, for every action to be measured, the right name from Google Analytics’ recommended events, and fixing its parameters, when it’s sent and the report it feeds in a single table before any code. Recommended events aren’t sent automatically because they need extra context to be meaningful; to get the most detail in reports and benefit from future features, they must be sent with their recommended parameters.⁴ We cover key events and reports on our Google Analytics 4 page.

In a property that sends lead events, the Lead acquisition report fills up; in a property that sends sales events, the Ecommerce purchases report does.⁴ After setup, we verify events with DebugView and the real-time report.⁴ The event code generator on this page produces a dataLayer.push draft for the recommended event you choose.

How are ecommerce events measured with GTM?

Ecommerce events are sent to the dataLayer with an items array describing the product and cart, and passed to Google Analytics in Tag Manager with a GA4 event tag. In Google’s setup, the tag type is “Google Analytics: GA4 Event”, the built-in {{Event}} variable is used for the event name, and under More Settings › Ecommerce, “Send Ecommerce data” is checked with Data Layer selected as the data source.⁵

An items array takes up to 200 elements; up to 27 custom parameters can be added alongside the defined ones.⁵ For events that send a value, the currency is specified at the event level; for purchase and refund events, the order number is sent with the required transaction_id parameter.⁵ It’s recommended to send every ecommerce parameter you have data for, even if it’s optional.⁵

How is Consent Mode v2 set up in GTM?

In Tag Manager, Consent Mode is set up with a tag created from the consent management platform’s (CMP) template in the Community Template Gallery, or from a template written with Tag Manager’s consent APIs; the route Google recommends is the CMP template.⁷ This tag sets the default consent state before other tags, and updates the state when the visitor makes a choice; Google tags adjust their behavior to that state.⁶⁸ The November 2023 update added the ad_user_data and ad_personalization parameters; Google refers to this version as “consent mode v2” and announced the change as part of enforcing its EU user consent policy more strictly.⁷ Under this policy, advertisers that receive data from users in the European Economic Area must collect those users’ consent and pass consent signals to Google; an advertiser already using Consent Mode and not running personalized advertising doesn’t need to take further action.¹³ Consent Mode can be implemented in two ways:

The “Consent Initialization – All Pages” trigger that comes with every web container is for tags that set or update the consent state, and fires before all other tags, including Initialization triggers.⁸ Google asks that consent settings not be made with custom HTML tags, and that Tag Manager’s consent APIs (setDefaultConsentState, updateConsentState) be used instead; gtag commands can wait in the queue and may not be processed before the next event.³⁷ The order of the code matters too: if the default consent command doesn’t come before the commands that send measurement, the defaults don’t work.⁷

The Google tag, GA4, Google Ads, Floodlight and Conversion Linker tags have built-in consent checks.⁶ For tags without this check, “Require additional consent for tag to fire” is selected under the tag’s Advanced Settings › Consent Settings; the tag fires only if all the specified consent types are “granted” at the moment it’s triggered.⁸ The Consent Overview page, enabled from container settings, shows tags with and without consent settings in two lists.⁸

How are changes tested before release?

Every change is first tested in preview and debug mode, then released with a version that has a name and description. Preview mode lets you browse the site as if the container’s unpublished draft were live; the previewed site connects to Tag Assistant, and you can see which tag fires in which order.⁹ The debug interface is visible only in the browser that opened preview, or to the people preview was shared with; visitors don’t see it.⁹ Because the preview link can be shared, we can work in the same session as the site’s developer.⁹

Changes made in a workspace don’t take effect on the site until they’re published; every publish saves a version of the container.¹⁰ A version is a snapshot of the container at a specific moment; after a faulty release, a previous version can be republished, and the publishing history shows who published which version and when.¹⁰ What we look at in every preview:

1. Event: did the expected event land in the dataLayer with the right name, and only once?
2. Tag: did the tag tied to the event fire, and did tags that shouldn’t fire stay silent?
3. Variable: did the value, currency and form ID pass through correctly?
4. Consent: did the tag behave according to the consent state the visitor chose?
5. Platform: did the event appear in GA4’s DebugView and on the relevant ad platform?

We write version names so they say what changed, such as “GA4 generate_lead: quote form success event”; the Tag Manager Help Center also recommends that the version name and description make the change understandable.¹⁰

How is a container kept clean and secure?

A container stays both readable and secure when permissions are given per person, unused items are cleared out and custom code is kept to a minimum. At container level, there are four permissions alongside “no access”:¹¹

Publish permission can be given to a small, experienced group able to review changes; the Approvals feature is only available in Tag Manager 360, part of Google Marketing Platform.¹⁰ As the number of tags, triggers and variables grows, or custom HTML tags get bigger, a size indicator can appear on the Versions page; if the value is above 70%, Google recommends improving the configuration.¹² The improvement routes in the documentation: combining similar tags into a single tag with a Lookup Table variable, deleting unused items, and reducing custom HTML tags and custom JavaScript variables in favor of supported templates.¹²

Another route is moving some tags to a tagging server; among the benefits of this route, Google lists a faster page with less third-party code, and the ability to remove data such as the IP address before it reaches the provider.¹² We cover the architecture and its cost on our server-side tracking page.

How Google Tag Manager consulting works in the first 30 days

The first 30 days follow a four-week sequence, from inventory to release:

1. Week 1 · Inventory: the tags, triggers, variables, consent settings and permissions on the site and in the container are mapped out; tags firing twice are flagged.
2. Week 2 · Event plan: the actions to measure are written with event name, parameters and when they’re sent, and approved with you.
3. Week 3 · Setup: dataLayer events are added to the site, tags and triggers are set up in a separate workspace, and Consent Mode is connected; every step is tested in preview.
4. Week 4 · Release and first reading: changes are released with a named version; events are tracked in GA4 and on ad platforms, and differences are reported.

How to choose a Google Tag Manager consultant or agency

Adding the container snippet takes minutes; the hard part is building a setup that is still readable a year later, respects consent and counts correctly. The three usual options for who does a GTM setup compare like this:

1. Account ownership: the Tag Manager account and container are opened in your company’s name; admin rights stay with you, and the partner works with container-level permissions.
2. A written event plan: each event’s name, parameters and firing moment are set in a table before any code and handed over to you.
3. Measuring success: forms and purchases are measured when the action actually completes, not on a button click.
4. Consent setup: the partner can explain which trigger sets the consent state and in what order, without falling back on a custom HTML tag.
5. Release discipline: every change is tested in preview and released with a named version that says what changed.

What drives Google Tag Manager setup pricing?

Google offers Tag Manager free of charge (Google Marketing Platform: Tag Manager); the price depends on the scope of setup and maintenance:

We work out the scope together in the first meeting and then send a written proposal; one-off setup and monthly maintenance are separate items. If a paid service such as a consent management tool is needed, it’s opened in your name and paid directly to the provider.

Google Tag Manager setup pricing: estimated ranges

Estimated one-off range, excluding VAT; scope is confirmed in a written proposal after the first meeting. As of October 2026.

If you’d like to read your container together, pick a meeting day that suits you below; in the first meeting we work out which events are measured and which are missing.