Glossary · Traffic sources & UTMs
What is referrer?
A referrer is the address of the web page that linked a visitor to the current page, sent by the browser in the HTTP Referer header and exposed to scripts as document.referrer.
The header is famously misspelled "Referer" — a typo in the original 1996 HTTP specification that stuck. The Referrer-Policy header that controls it is spelled correctly.
Also called: HTTP Referer, Referring domain
Updated
How does the referrer work?
When a visitor clicks a link, the browser requests the new page and includes the previous page's address in the request. How much of that address is sent depends on the linking page's Referrer-Policy. Modern browsers default to strict-origin-when-cross-origin: the full URL for same-site navigation, only the origin (https://example.com/) for cross-site navigation, and nothing when going from https to http.
| Referrer-Policy | What another site receives |
|---|---|
strict-origin-when-cross-origin (default) | Origin only, e.g. https://news.ycombinator.com/ |
no-referrer | Nothing — the visit looks direct |
origin | Origin only, even on https→http |
unsafe-url | Full URL including path and query (leaks data; avoid) |
Referrer example
A visitor clicks your link in a Reddit thread. Your analytics receives https://www.reddit.com/ as the referrer — the domain, but not the thread, because of the default policy. If the same link is opened from the Reddit app, there may be no referrer at all and the visit is counted as direct traffic.
Why the referrer matters
It's the raw input for almost every traffic source report. Channel grouping, referral reports and most attribution models start from the referrer whenever there are no UTM parameters. Knowing its limits explains why your source data has gaps.
Common referrer pitfalls
- Assuming full URLs. Cross-site referrers are almost always origin-only now; page-level referral data mostly comes from UTMs.
- Apps send nothing. Links tapped in native apps arrive without a referrer.
- Wrappers and redirects.
t.co,lnkd.in,l.facebook.comand email trackers replace the original source with their own. - Your own policy. Setting
no-referrersite-wide to be private also hides you in every site you link to, including partners who'd credit you.
How VisitTrack uses the referrer
The VisitTrack script sends document.referrer with the first pageview of each session. The server reduces it to a hostname (stripping www.), stores that as the session's source and classifies it into direct, search, social, AI or referral. UTM tags, when present, are stored next to it, and the visitor's first referrer becomes the source credited for later payments in revenue attribution. Try any domain in the referrer channel checker.
Frequently asked questions
Why is it spelled "referer"?
It was misspelled in the original HTTP specification in 1996 and kept for compatibility. The HTTP header is Referer; the JavaScript property (document.referrer) and the Referrer-Policy header use the correct spelling.
Why is the referrer empty?
The visitor typed the URL, used a bookmark, clicked in an app or email client, came from an https page to an http page, or the linking page set a no-referrer policy.
Related terms
- Referral trafficReferral traffic is visits that arrive by clicking a link on another website that isn't a search engine, social network or ad — for example a blog post, directory, forum or partner site that links to you.
- Direct trafficDirect traffic is any visit that arrives with no referrer and no campaign parameters, so the analytics tool can't tell where it came from and files it as "direct" or "(none)".
- Dark socialDark social is traffic from links shared through private channels — messaging apps, email, Slack, text messages, closed communities — that arrives without a referrer, so analytics tools record it as direct traffic.
- Channel groupingChannel grouping is the set of rules an analytics tool uses to sort every visit into a marketing channel — such as direct, organic search, paid search, social, email or referral — based on its referrer, UTM parameters and ad click ids.
- utm_sourceutm_source is the UTM parameter that identifies the specific site, platform or publisher that sent a visit — for example google, newsletter, x or a partner's name.
Tools and guides
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