Google Tag Manager Implementation Reference

Detailed guide for implementing tracking via Google Tag Manager.

Container Structure (tags, triggers, variables)
Naming Conventions
Data Layer Patterns
Common Tag Configurations (GA4 configuration tag, GA4 event tag, Facebook pixel)
Preview and Debug
Workspaces and Versioning
Consent Management
Advanced Patterns (tag sequencing, exception handling, custom JavaScript variables)

Container Structure

Triggers

Triggers define when tags fire.

Built-in triggers:

Page View: All Pages, DOM Ready, Window Loaded
Click: All Elements, Just Links
Form Submission
Scroll Depth
Timer
Element Visibility

Custom triggers:

Custom Event (from dataLayer)
Trigger Groups (multiple conditions)

Variables

Variables capture dynamic values.

Built-in (enable as needed):

Click Text, Click URL, Click ID, Click Classes
Page Path, Page URL, Page Hostname
Referrer
Form Element, Form ID

User-defined:

Data Layer variables
JavaScript variables
Lookup tables
RegEx tables
Constants

Naming Conventions

Recommended Format

[Type] - [Description] - [Detail]

Tags:
GA4 - Event - Signup Completed
GA4 - Config - Base Configuration
FB - Pixel - Page View
HTML - LiveChat Widget

Triggers:
Click - CTA Button
Submit - Contact Form
View - Pricing Page
Custom - signup_completed

Variables:
DL - user_id
JS - Current Timestamp
LT - Campaign Source Map

Data Layer Patterns

Basic Structure

// Initialize (in <head> before GTM)
window.dataLayer = window.dataLayer || [];

// Push event
dataLayer.push({
  'event': 'event_name',
  'property1': 'value1',
  'property2': 'value2'
});

Page Load Data

// Set on page load (before GTM container)
window.dataLayer = window.dataLayer || [];
dataLayer.push({
  'pageType': 'product',
  'contentGroup': 'products',
  'user': {
    'loggedIn': true,
    'userId': '12345',
    'userType': 'premium'
  }
});

Form Submission

document.querySelector('#contact-form').addEventListener('submit', function() {
  dataLayer.push({
    'event': 'form_submitted',
    'formName': 'contact',
    'formLocation': 'footer'
  });
});

Button Click

document.querySelector('.cta-button').addEventListener('click', function() {
  dataLayer.push({
    'event': 'cta_clicked',
    'ctaText': this.innerText,
    'ctaLocation': 'hero'
  });
});

E-commerce Events

// Product view
dataLayer.push({ ecommerce: null }); // Clear previous
dataLayer.push({
  'event': 'view_item',
  'ecommerce': {
    'items': [{
      'item_id': 'SKU123',
      'item_name': 'Product Name',
      'price': 99.99,
      'item_category': 'Category',
      'quantity': 1
    }]
  }
});

// Add to cart
dataLayer.push({ ecommerce: null });
dataLayer.push({
  'event': 'add_to_cart',
  'ecommerce': {
    'items': [{
      'item_id': 'SKU123',
      'item_name': 'Product Name',
      'price': 99.99,
      'quantity': 1
    }]
  }
});

// Purchase
dataLayer.push({ ecommerce: null });
dataLayer.push({
  'event': 'purchase',
  'ecommerce': {
    'transaction_id': 'T12345',
    'value': 99.99,
    'currency': 'USD',
    'tax': 5.00,
    'shipping': 10.00,
    'items': [{
      'item_id': 'SKU123',
      'item_name': 'Product Name',
      'price': 99.99,
      'quantity': 1
    }]
  }
});

Common Tag Configurations

GA4 Configuration Tag

Tag Type: Google Analytics: GA4 Configuration

Settings:

Measurement ID: G-XXXXXXXX
Send page view: Checked (for pageviews)
User Properties: Add any user-level dimensions

Trigger: All Pages

GA4 Event Tag

Tag Type: Google Analytics: GA4 Event

Settings:

Configuration Tag: Select your config tag
Event Name: {{DL - event_name}} or hardcode
Event Parameters: Add parameters from dataLayer

Trigger: Custom Event with event name match

Facebook Pixel - Base

Tag Type: Custom HTML

<script>
  !function(f,b,e,v,n,t,s)
  {if(f.fbq)return;n=f.fbq=function(){n.callMethod?
  n.callMethod.apply(n,arguments):n.queue.push(arguments)};
  if(!f._fbq)f._fbq=n;n.push=n;n.loaded=!0;n.version='2.0';
  n.queue=[];t=b.createElement(e);t.async=!0;
  t.src=v;s=b.getElementsByTagName(e)[0];
  s.parentNode.insertBefore(t,s)}(window, document,'script',
  'https://connect.facebook.net/en_US/fbevents.js');
  fbq('init', 'YOUR_PIXEL_ID');
  fbq('track', 'PageView');
</script>

Trigger: All Pages

Facebook Pixel - Event

Tag Type: Custom HTML

<script>
  fbq('track', 'Lead', {
    content_name: '{{DL - form_name}}'
  });
</script>

Trigger: Custom Event - form_submitted

Preview and Debug

Preview Mode

Click "Preview" in GTM
Enter site URL
GTM debug panel opens at bottom

What to check:

Tags fired on this event
Tags not fired (and why)
Variables and their values
Data layer contents

Debug Tips

Tag not firing:

Check trigger conditions
Verify data layer push
Check tag sequencing

Wrong variable value:

Check data layer structure
Verify variable path (nested objects)
Check timing (data may not exist yet)

Multiple firings:

Check trigger uniqueness
Look for duplicate tags
Check tag firing options

Workspaces and Versioning

Workspaces

Use workspaces for team collaboration:

Default workspace for production
Separate workspaces for large changes
Merge when ready

Version Management

Best practices:

Name every version descriptively
Add notes explaining changes
Review changes before publish
Keep production version noted

Version notes example:

v15: Added purchase conversion tracking
- New tag: GA4 - Event - Purchase
- New trigger: Custom Event - purchase
- New variables: DL - transaction_id, DL - value
- Tested: Chrome, Safari, Mobile

// Default state (before consent)
gtag('consent', 'default', {
  'analytics_storage': 'denied',
  'ad_storage': 'denied'
});

// Update on consent
function grantConsent() {
  gtag('consent', 'update', {
    'analytics_storage': 'granted',
    'ad_storage': 'granted'
  });
}

Enable Consent Overview in Admin
Configure consent for each tag
Tags respect consent state automatically

Advanced Patterns

Tag Sequencing

Setup tags to fire in order: Tag Configuration > Advanced Settings > Tag Sequencing

Use cases:

Config tag before event tags
Pixel initialization before tracking
Cleanup after conversion

Exception Handling

Trigger exceptions - Prevent tag from firing:

Exclude certain pages
Exclude internal traffic
Exclude during testing

Custom JavaScript Variables

// Get URL parameter
function() {
  var params = new URLSearchParams(window.location.search);
  return params.get('campaign') || '(not set)';
}

// Get cookie value
function() {
  var match = document.cookie.match('(^|;) ?user_id=([^;]*)(;|$)');
  return match ? match[2] : null;
}

// Get data from page
function() {
  var el = document.querySelector('.product-price');
  return el ? parseFloat(el.textContent.replace('$', '')) : 0;
}

Command Palette

coreyhaines31/analytics-tracking — references/gtm-implementation.md