What is Referrer?
The referrer is the URL of the page that linked a visitor to yours, reported by the browser in the Referer header. It is how analytics tools attribute traffic to sources without any tracking. Modern browser defaults trim it to the origin, and several common paths — apps, email clients, HTTPS to HTTP — send nothing at all.
What the browser actually sends
Since browsers adopted strict-origin-when-cross-origin as the default referrer policy, a cross-site link reports only the origin — https://example.com, not the article that carried the link. You learn the site, not the page.
Referrers are absent entirely when:
- The visitor came from a native app that opens links in its own web view.
- The link was in an email client or a messaging app.
- The source page sets a restrictive
Referrer-Policyof its own. - The visitor typed the address, used a bookmark, or restored a tab.
All of these land in direct traffic, which is therefore not a channel but a bucket of everything unidentifiable. Treat a large direct share as missing information, not as brand strength.
Referrer spam
Fake referrers have been injected into analytics for years, either to appear as links in public reports or simply as a side effect of scanning. sonex filters known spam referrers during ingestion rather than at query time, so they never enter your data and cannot skew a historical report you run later.
Referrers and campaigns together
The referrer tells you which site sent traffic. It cannot tell you which campaign, which creative, or which position in a newsletter — a browser has no way to know any of that.
That is what UTM parameters are for. Use referrers for the traffic you did not tag, which is most of the honest, earned kind, and UTMs for the traffic you did.