Google Tag Manager

Overview

Expertise for Google Tag Manager (GTM) covering container setup, tag configuration, triggers, variables, data layer implementation, debugging, custom templates, and API automation. See the reference files below for detailed guidance on each topic.

When to Use This Skill

Invoke when setting up or configuring GTM containers, tags, triggers, or variables; implementing the data layer; debugging with Preview mode or Tag Assistant; building custom templates; automating via the REST API; or optimising container performance and consent management.

Quick Start

1. Create a GTM account at tagmanager.google.com
2. Create a container (Web, iOS, Android, or Server)
3. Install the container snippet - see setup.md
4. Configure tags, triggers, and variables
5. Test in Preview mode - see debugging.md
6. Publish

Basic Tag Configuration

Example: Google Tag (GA4)
Tag Type: Google Tag
Tag ID: G-XXXXXXXXXX
Trigger: All Pages

See tags.md for comprehensive tag documentation.

Data Layer Push

window.dataLayer = window.dataLayer || [];
dataLayer.push({
  'event': 'custom_event',
  'category': 'engagement',
  'action': 'button_click',
  'label': 'CTA Button'
});

See datalayer.md for data layer patterns.

Core Concepts

Tags are snippets of code that execute on your site (e.g., GA4, Google Ads, Facebook Pixel).

Triggers define when tags fire (e.g., page views, clicks, form submissions).

Variables capture dynamic values for use in tags and triggers (e.g., page URL, click text, data layer values).

User Action --> Trigger Fires --> Tag Executes --> Data Sent
     ^                                    |
     |                                    v
     +--- Variables provide values -------+

Common Workflows

GA4 Page View Tracking

1. Create Google Tag with your GA4 Measurement ID (formerly the "GA4 Configuration" tag type)
2. Set trigger to "All Pages"
3. Test in Preview mode, verify in GA4 DebugView
4. Publish

Form Submission Tracking

1. Create Form Submission trigger
2. Create GA4 Event tag (form_submit) with form ID/name as parameter
3. Test in Preview mode and publish

E-commerce Tracking

1. Implement data layer with e-commerce events - see datalayer.md
2. Create data layer variables and GA4 Event tags for each event
3. Map variables to event parameters
4. Test complete purchase flow and publish

Debug Tag Not Firing

1. Enable Preview mode and perform the action
2. Check "Tags Not Fired" section and review trigger conditions
3. Verify data layer values, fix conditions, and retest
4. See debugging.md for detailed workflows

Technical Constraints

ES5 Required: Custom JavaScript Variables and Custom HTML Tags must use ES5 syntax (var, function(), string concatenation). Custom Templates support some ES6. See best-practices.md for details and workarounds.

RE2 Regex: GTM uses RE2 regex - no lookahead, lookbehind, or backreferences. See best-practices.md for supported patterns.

Quick Reference

Built-in Variables to Enable

• Page URL, Page Path, Page Hostname
• Click Element, Click Classes, Click ID, Click URL, Click Text
• Form Element, Form ID, Form Classes
• Scroll Depth Threshold, Scroll Direction

Common Trigger Types

Page View, Click (All Elements / Just Links), Form Submission, Custom Event, History Change (SPAs), Timer, Scroll Depth

Essential Data Layer Events

// Page view
dataLayer.push({ 'event': 'page_view' });

// User login
dataLayer.push({ 'event': 'login', 'method': 'Google' });

// Purchase
dataLayer.push({
  'event': 'purchase',
  'ecommerce': {
    'transaction_id': 'T12345',
    'value': 99.99,
    'currency': 'AUD',
    'items': [...]
  }
});

Reference Files

Topic	Reference File
Container setup	setup.md
Tag configuration	tags.md
Trigger configuration	triggers.md
Variable configuration	variables.md
Data layer	datalayer.md
Debugging	debugging.md
Best practices, naming, performance, security	best-practices.md
Custom templates	custom-templates.md
API automation	api.md

External Resources

• GTM Help Center
• GTM Developer Documentation
• GA4 Implementation Guide
• GTM API Reference