Skip to content
AnyTrack AnyTrack Knowledge Base

atrefid

atrefid is the URL parameter that carries a click ID across domains in cross-domain tracking. The Tracking Tag adds it to links that point at the destination domain. Its value is the 34-character Click ID of that link. A conversion recorded on the destination Property can then attribute back to the ad click that landed on the source Property.

How atrefid behaves

Section titled “How atrefid behaves”
  • The Tag adds it to the link in the browser, after the page loads. For links that appear later, it adds it when the page content changes. It does not wait for the click. The HTML that the server sends does not contain it, so verify it by inspecting the link in your browser developer tools or by clicking the link, not by viewing source.
  • It is used when Sync Conversions is ON and at least one event name is selected. With Sync Conversions OFF, or with no event names selected, cross-domain links carry atclid instead. Both parameters carry the same 34-character Click ID.
  • All cross-domain settings live on the source Property: the destination-domain list, the Sync Conversions toggle, and the synced event-names allowlist.

How atrefid returns the conversion to the source Property

Section titled “How atrefid returns the conversion to the source Property”

With Sync Conversions ON, atrefid is a round trip, not a one-way handoff:

  1. The visitor clicks the cross-domain link. The source Property tracks the OutboundClick event.
  2. atrefid and its value pass to the destination domain in the page URL.
  3. The destination page carries the Tracking Tag. The Tag sends events with the page URL, so the atrefid value reaches AnyTrack.
  4. AnyTrack reads the Property ID in the atrefid value and finds the source Property. AnyTrack ignores traffic of the same Property. If the destination belongs to another AnyTrack account, the destination host must be in the destination-domain list of the source Property.
  5. If the event name is in the synced event-names allowlist of the source Property, AnyTrack copies the conversion to the source Property.
  6. The source Property attributes the conversion to the original session and its UTM parameters, and sends it to the connected ad platforms through their Conversion API.

This return leg is why cross-domain attribution credits the campaign that produced the first click, even though the conversion happened on the other domain. AnyTrack does not copy a conversion whose event name is outside the allowlist.

What atrefid is not

Section titled “What atrefid is not”

If you see _atid on URLs, it is unrelated to atrefid. The Tracking Tag writes _atid into the current page URL for click-ID collection on the same site, and it has nothing to do with cross-domain tracking.

Frequently asked questions

FAQ was last reviewed on 2026-11-08

I don't see atrefid in my page's HTML source. Is it missing?
No. The Tracking Tag adds atrefid to the link in the browser, after the page loads. The HTML that the server sends does not contain it, so View Source does not show it. Inspect the link in your browser developer tools, or click the link and read the destination URL.
When do cross-domain links carry atclid instead of atrefid?
When Sync Conversions is OFF, or when no event names are selected for it, the links carry atclid. When Sync Conversions is ON with at least one event name (the standard cross-domain setup), they carry atrefid. Both parameters carry the 34-character Click ID.

Related terms

Cross-Domain Tracking The setup atrefid exists for Property atrefid links a visitor journey across two independent Properties AutoTag Appends the parameter to cross-domain links atclid The parameter cross-domain links carry instead when Sync Conversions is OFF or has no event names selected