What Is a Referrer?

A referrer identifies the web page from which a request came. In HTTP, the historical header name is spelled Referer. A browser may send the previous page address when someone follows a link, but the information depends on referrer policy, protocol, browser behavior, and privacy settings.

Why Can a Referrer Be Missing?

A visit may arrive without a referrer when a link opens from a chat app, document, bookmark, typed URL, or environment that limits referral information. Some services also remove the path and send only the origin to reduce data leakage. An empty referrer does not necessarily mean the visitor manually typed the address.

Referrer vs UTM Parameters

A referrer comes from the technical request context and is not completely controlled by a marketer. A UTM parameter is deliberately added to the URL to label source, medium, and campaign. The two can complement each other: the referrer offers a clue about the web origin, while UTM values provide the campaign structure planned by a team.

Recommended Practices

1. Use UTM tags on campaign links you control
2. Keep personal data out of URL parameters
3. Group empty referrers cautiously
4. Compare the result with distribution context
5. Document redirects that may affect the data
6. Do not infer a person's identity from the referrer

s.id analytics may show referral information according to availability and plan, but the result still depends on what a visitor's device and application pass to the service.

Reference

• RFC 9110: Referer field