A gclid inside an ef_id
Click a Google search ad from a brand that runs Adobe Advertising, and the landing page URL can end in ef_id= plus a long value that starts like a gclid and finishes with :G:s. Adobe documents why. For Google Ads search clicks the format is {gclid}:G:{s}: Google's own click ID, then G, then s for the search network type. Microsoft Advertising clicks follow the same pattern with Microsoft's click ID, msclkid, at the front.
The other shape
Display ads, and search ads on other engines, use a different layout: {amovid}:{ts}:{channel}. The first field is the Adobe Advertising visitor ID, which Adobe says is also known as the surfer ID. Next comes a timestamp Adobe Advertising generates, and last is one letter for how the ad reached the person:
- d: a click on a display ad bought through Adobe's DSP
- i: an impression of one of those display ads, with no click
- s: a click on a search ad
So an ef_id ending in :d came from a display ad click, and one ending in :G:s came from a Google or Microsoft search ad.
Where Adobe Analytics picks it up
Adobe calls the value the AMO EF ID, "a unique token that Adobe Advertising uses to associate activity with an online click or ad exposure at a visitor level." The Analytics for Advertising integration fills a dimension of that name automatically, with no variable for the site to set. For click-throughs, Adobe reads it from the ef_id parameter in the page URL, usually on the page where ad traffic enters the site. Its sibling on the same links, s_kwcid, describes the ad and keyword, and Adobe says those values are less granular than EF IDs.
The lowercase trap
Adobe's documentation warns: "EF IDs are case-sensitive. If your implementation forces URL tracking to lowercase, then Adobe Advertising does not recognize the EF ID." A redirect or tag rule that lowercases URLs breaks the match between ad and visit, and nothing on the page looks wrong. Visitors see an identical page without ef_id, and since Adobe ties the token to activity at a visitor level, it is worth removing before you share the link. For advertisers, a click that arrives without it no longer carries the ID Adobe reads from the URL.