Hands-on module
Reliability & monitoring
Turn errors and Core Web Vitals into events so you know when tracking breaks.
Tracking is only useful if you can trust it, which means knowing when the page breaks and how fast it loads. This module turns failures and performance into events you can tag.
You'll catch uncaught JavaScript errors with GTM's built-in trigger, close the promise-rejection blind spot it leaves with a small listener, and push Core Web Vitals to the dataLayer so LCP, CLS and INP land in GA4.
What you'll learn
- Catch uncaught errors with the JavaScript Error trigger (gtm.pageError)
- Cover async failures by listening for unhandledrejection and pushing an event
- Read Core Web Vitals with PerformanceObserver and send them to GA4
- Send the Error built-in variables so you can see what broke
Lessons
- 1→
The Debugging Mindset
Preview mode is not proof. Verify at every layer.
- 2→
Tag Assistant Preview, In Depth
Tags, Variables, the dataLayer, and the message list.
- 3→
Reading Requests In DevTools
The Network tab is the source of truth for what was sent.
- 4→
Console, Elements & Application
Inspect the dataLayer, find selectors, check cookies.
- 5→
Helper Tools & Extensions
Faster debugging with the right add-ons.
- 6→
A Field Guide To Common Bugs
The handful of issues behind most broken setups.
- 7→
A Pre-Publish QA Checklist
A repeatable routine before you hit Publish.
- 8→
JavaScript Error Tracking
Trigger a page error and catch it with GTM's JavaScript Error trigger.
- 9→
Promise Rejection Tracking
Catch unhandledrejection beyond gtm.pageError.
- 10→
Web Vitals To DataLayer
Push LCP / CLS / INP via PerformanceObserver and tag them.
- 11→
Reliability & Monitoring: Recap And Verify
Recap every lesson, then check your whole container in one pass.