The essentials
- Definition: the referrer is the URL of the page a visitor clicked to reach your site, passed on by the browser in the HTTP header
Referer. - In GA4: it determines the source and the channel (Referral, Organic Search, Organic Social), unless UTMs or a gclid say otherwise.
- Often missing: mobile apps, emails, documents, browser privacy policies; that traffic then falls into "Direct".
- How to use it: measuring partnerships, press coverage, directories, and traffic coming from AI.
The referrer (the spelling "Referer", with one r, comes from a historic typo in the HTTP specification) is the address of the page a visitor came from. When someone clicks a link to your site, their browser generally passes on the URL of the page they started from. GA4 reads that information to attribute the session to a source and a channel. It is the basic mechanism of acquisition measurement, and also one of the most fragile.
How GA4 uses the referrer
| Referrer received | Source / medium attributed | GA4 channel |
|---|---|---|
| google.fr (organic result) | google / organic | Organic Search |
| facebook.com, linkedin.com, instagram.com | facebook / referral, recognised as social | Organic Social |
| lemonde.fr, a blog, a directory | lemonde.fr / referral | Referral |
| chatgpt.com, perplexity.ai | chatgpt.com / referral | Referral (to be grouped into a custom "AI" channel) |
| None | (direct) / (none) | Direct |
UTM parameters and the Google Ads gclid take priority over the referrer: that is what lets you tell a newsletter (utm_medium=email) apart from an ordinary link. Without them, GA4 relies on the referrer, and without a referrer, everything becomes "Direct". The full set of rules is in sources, mediums and UTMs.
Why the referrer is often missing
- Mobile apps : links opened from the Instagram, Facebook or LinkedIn app, or from a messaging app, don't always pass on the original URL.
- Emails and documents : a click from Outlook, the Gmail app, a PDF or a Word file has no web page of origin.
- Referrer policy : browsers apply by default
strict-origin-when-cross-origin, which passes on only the domain (not the full page) between different sites; some sites hide everything (no-referrer). - Going from HTTPS to HTTP : the referrer is stripped for security reasons.
- Redirects : some shorteners or intermediate trackers erase the origin.
The consequence: GA4's "Direct" channel contains a lot of traffic that isn't direct at all. On a small business site, a share of 15 to 25% is normal; beyond 40%, you have untagged campaigns.
Reading and using referral traffic
In Reports > Acquisition > Traffic acquisition, with the "Session source" dimension filtered on the Referral channel, you see every site sending you visitors, with their engagement and their conversions. Three uses:
- Measuring a partnership or a press article : how many sessions, what engagement rate, how many leads. A link bringing 200 engaged visits a month is worth more than its SEO effect alone.
- Spotting unexpected links : a forum, a directory, a mention in a publication you didn't know about. It is also a source of ideas for netlinking.
- Tracking traffic from AI : chatgpt.com, perplexity.ai, gemini.google.com and copilot.microsoft.com show up as referrals. Group them into a custom channel, as explained in measuring GEO with GA4.
Referrer spam and the referrers to exclude
Two nuisances worth knowing about. Referrer spam (bots sending fake visits with an advertising domain as the referrer) has fallen a long way with GA4, but it can reappear: filter it out with an exclusion rule if an unknown source generates sessions with no engagement. The referrers to exclude are your payment providers (Stripe, PayPal) and your own domains: without an exclusion, every return from payment opens a new session attributed to the provider. The setting is described in setting GA4 up properly from the start.
The related terms (source, medium, channel, direct) are defined in the Google Analytics glossary.
How GreenRed helps
Rather than juggling several tools, GreenRed's Traffic module brings these metrics together in a single dashboard, compares them over time and tells you which actions come first. You can try it free, with no card, from the Pricing.
Frequently asked questions
What is the difference between a referrer and a referral?
The referrer is the technical information (the URL of the originating page, passed on by the browser). Referral is the name of the GA4 channel that holds sessions arriving from a third-party site by a link, excluding recognised search engines and social networks. The referrer is what determines the channel, Referral among them.
Why is my direct traffic so high in GA4?
Because the Direct channel receives every session with no referrer and no campaign parameter: clicks from mobile apps, emails, documents, or links whose origin the browser hides. Tag your campaigns with UTMs to reduce that share; 15 to 25% direct remains normal.
How do I see traffic from ChatGPT in GA4?
In Traffic acquisition, with the Session source dimension, look for chatgpt.com (and perplexity.ai, gemini.google.com, copilot.microsoft.com). Those sources arrive in the Referral channel. Create a custom channel group called "Generative AI" to track them together over time.
Can I hide my own site's referrer?
Yes, with the meta referrer tag or the Referrer-Policy header (no-referrer, for example). The sites you link to then won't see where their visitors came from. That's useful for protecting confidential URLs, but it deprives your partners of any measure of what you send them.