google-tagmanager

Google Tag Manager

Pick the reference file from the table at the end and read it before answering anything beyond the basics below.

The bundled gtm-mcp-server is Stape's hosted GTM MCP server (a third party, not Google). Its tools can create, update and delete tags, triggers, variables and other entities, and create and publish container versions. Before calling a delete or publish action, state what will change and in which container and workspace, and let the user approve it.

Quick Start

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

Basic Tag Configuration

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

See tags.md for 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.

Common Workflows

GA4 Page View Tracking

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

Form Submission Tracking

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

E-commerce Tracking

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

Consent Mode v2

Four consent types gate Google tags: ad_storage, analytics_storage, ad_user_data and ad_personalization (the last two are required for EEA/UK ad measurement and personalisation).

Add the CMP's template from the Community Template Gallery (or build one with the setDefaultConsentState / updateConsentState template APIs - templates call these rather than gtag('consent', ...)).
Fire it on the Consent Initialization - All Pages trigger so defaults (usually denied, optionally per region, with wait_for_update) are set before any other tag.
The CMP updates consent when the user chooses; Google tags adjust automatically. For non-Google tags, set Additional consent checks in each tag's Consent Settings and use the container's Consent Overview to confirm every tag is covered.
Choose basic mode (tags blocked until consent) or advanced mode (Google tags load and send cookieless pings while denied).
In Preview, the Consent tab for each event shows default and update states - confirm defaults appear on Consent Initialization before the first tag fires.

Debug Tag Not Firing

Enable Preview mode and perform the action
Check "Tags Not Fired" section and review trigger conditions
Verify data layer values, fix conditions, and retest
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 - clear the previous ecommerce object first
dataLayer.push({ 'ecommerce': null });
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
Server-side containers: hosting, custom domain, clients, GA4 server tag	server-side.md

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