Link domain dimension
Link domain is the dimension that records the destination host of a clicked outbound link — the domain portion of link_url. GA4 enhanced measurement sets it on the click event so you can group outbound traffic by where it goes (a partner, a payment provider, a social network) without parsing full URLs. What counts as outbound, and therefore what appears here, depends on your cross-domain measurement configuration.
What this means
The link domain dimension is the host extracted from a clicked outbound link's URL. Enhanced measurement provides it as link_domain on the click event, letting you aggregate many distinct destination URLs under a single domain in reports.
This is the right grain for questions like 'how much traffic do we send to each partner?' that link_url is too granular to answer cleanly.
Cross-domain interplay
GA4 fires the outbound click event only for links that leave your configured domains. If you add a property or subdomain to cross-domain measurement, clicks to it stop being outbound and disappear from link_domain; remove it and they reappear.
So an unexpected own-domain value here is a signal to review which hosts your cross-domain settings cover.
- Host portion of an outbound link's URL
- Coarser grouping than link_url
- Defined relative to cross-domain configuration
How it appears in analytics and logs
A link domain value is the host of a clicked external link. A domain you consider yours appearing here means it is not in your cross-domain configuration and is being treated as outbound.
Diagnostic use case
Use link domain to rank the external destinations your visitors leave to, grouping many specific URLs under one host.
What WebmasterID can help detect
WebmasterID can record the destination host of outbound clicks as first-party events, so leakage to partners is measurable without third-party cookies.
Common mistakes
- Ignoring cross-domain config when interpreting own-domain values.
- Treating link_domain as a count of unique destinations rather than hosts.
- Forgetting subdomains may be counted as outbound by default.
Privacy and accuracy notes
Link domain records a destination host, not a person. WebmasterID records outbound destinations first-party without tracking visitors onto the linked site.
Related pages
- Outbound link domain dimension
The outbound link domain is the external host a visitor clicked toward — for example partner.com when leaving your site. GA4 captures it as link_domain on click events when enhanced measurement's outbound clicks are on. This page explains derivation, the difference from referrer, and why some outbound clicks go uncounted.
- Link URL dimension: where outbound clicks go
Link URL is the dimension that records the destination of a clicked link. In GA4 it is populated by the click event from enhanced measurement, which fires on outbound links and carries link_url, link_domain, and link_text. It answers 'where did people leave to?', but its automatic scope is limited to links leaving your domain — internal and same-domain clicks need separate handling.
- The click event and outbound clicks
A click event records that a visitor activated a link or element. The most common analytics use is the outbound click — a click on a link leaving your domain — which a normal page_view can never capture because the destination is another site. This page covers what to record on a click, how outbound detection works, and which properties stay privacy-safe.
- CTA tracking
Measure outbound destinations by host first-party.
Sources and verification notes
- Google Analytics Help — [GA4] Enhanced measurement eventsDocuments the outbound click event and link_domain parameter.
Last reviewed 2026-06-24. Facts are checked against primary/official sources where available; uncertain specifics are marked “Data not yet verified” rather than guessed.