Event Parameter

An event parameter is an extra piece of detail attached to an event, describing something about how it happened.

Every event can carry parameters that add context: which page, which link, how much a purchase was worth. GA4 collects some automatically and lets you send your own, and you use them to break events down in reporting.

A page_view event carries a page_location parameter holding the URL. A purchase event carries a value parameter holding the order total and a currency parameter naming the currency.

A parameter you send is not a parameter you can report on. To slice by a custom parameter in standard reports, you have to register it as a custom dimension or metric first, and there are limits on how many. Sending it is only half the job.

The event says what happened. The parameter says the details.