Lesson 1 of 9
The Site You Inherit, Not The One You Planned
The measurement-planning course shows you how a clean dataLayer is supposed to look: agreed event names, the right keys on every push, fired once at the right moment. Almost no site you inherit looks like that. Instead you get a container someone else built, a dataLayer made of whatever the theme, a forms plugin, a chat widget and three years of rushed requests happened to push, and a request that sounds simple: "just track the demo form."
When there is no plan, the skill is not designing the data — it is investigating what already exists and working out how to get a trustworthy event out of it. Think of it as data archaeology: before you build anything, you dig, you observe what the page actually does, and only then do you decide how to capture it.
The planned world
- One agreed event name, documented
- Every key present and correctly typed
- Fires once, exactly when it should
- You build straight from the spec
The world you inherit
- Three events that could be 'the' submit
- Half the keys missing or empty strings
- Fires twice, or before the data exists
- You reverse-engineer it from behavior
This course is the field manual for that second world. The golden rule runs through all of it: observe before you build. The single most common mistake is to assume what the dataLayer contains, build a tag on that assumption, and ship something that quietly fires on the wrong events or sends blanks. Every lesson here is a way to replace an assumption with something you have actually watched happen.
Key takeaway
On a real site your first job is investigation, not configuration. Never tag against what you assume is in the dataLayer — tag against what you have watched it do.