Referrer
A request header carrying the address of the page a visitor came from, used to attribute a click to the place that published it.
Updated August 14, 2026
The referrer is a header a browser sends with a request, holding the address of the page that contained the link. A redirect service reads it to say where a click came from, which is how a traffic report fills in social networks, blogs and search engines without anyone tagging anything.
It is missing far more often than people expect, and each absence has a cause. A link opened from SMS or a messaging app has no referring page at all. A move from an https page to an http destination drops the header by design. Most sites now send only their origin rather than the full address, and privacy settings can suppress it entirely. So "direct" in a referrer breakdown is not one behaviour; it is every case where nobody said.
Because of that, referrer is evidence and UTM parameters are a record. Tag the links you publish yourself and keep the referrer for what you cannot tag — reshares, forums, places that picked the link up on their own.