What is Referrer?
A referrer (often seen as the HTTP Referer header) is the URL of the page a visitor came from before landing on your site. Analytics tools use it to determine where traffic originated—e.g., another website, search engine, or social network—and to classify visits as Referral or Direct. Knowing the referrer improves reporting, Attribution accuracy, and campaign ROI analysis.
What is referrer? In short: it’s the upstream page that sent the click.
How referrer works
When a user clicks a link, the browser typically sends the previous page’s address in the request header. Your analytics script (GA4, Plausible, Matomo, Simple Analytics, etc.) reads that value and stores it in the hit/session record. If the link also contains UTM parameters, those override plain referrer for channel and Campaign attribution. This data rolls up into metrics like Engagement Rate and Pages Per Session.
Common edge cases (why referrer is missing or truncated)
- Privacy & security settings. The site may set a strict
Referrer-Policyor userel="noreferrer", which removes the header entirely—visits may appear as Direct. - Protocol/host changes. Moving from HTTPS→HTTP or across domains without proper setup can drop or shorten referrers; use proper redirects and Cross-Domain Tracking.
- Apps & messengers. Many in-app browsers don’t pass full referrers; rely on UTM tagging.
- Cookies & sessionization. The first hit that defines a Session captures the referrer; later hits inherit it even if the header disappears. Respect storage rules with a robust First-Party Cookie design.
Quick reference
| Situation | What you’ll see in reports |
|---|---|
| Link with UTMs | Campaign/source from UTMs, not raw referrer |
| Cross-domain without linking fix | New session; origin may look like self-referral |
Strict referrer policy or noreferrer | Traffic shows as Direct |
Analyst tips
- Always tag campaigns with UTM to protect attribution, especially from social/apps.
- Audit “self-referrals”; they often signal broken cross-domain flows.
- Align your model choice (Attribution Model, e.g., Last Touch) with how referrers and UTMs are captured.
- For server-side pipelines or imports via Measurement Protocol, forward referrer info explicitly.