Click ID

A click ID is a unique string an ad platform appends to the destination URL when a user clicks an ad, for example Google Ads' gclid or Meta's fbclid. When that same identifier is later sent back to the platform alongside a conversion event, through a browser pixel or a conversion API, the platform can match the conversion to the specific click that caused it.

Click IDs serve a more precise version of what UTM parameters do for analytics tools: UTMs tell an analytics platform which campaign and channel drove a visit, while a click ID lets the advertising platform itself trace a conversion back to one exact click, which is what makes last-click attribution and other click-based models possible within a defined attribution window.

Click IDs matter because as browsers restrict cookies and cross-site tracking, they have become one of the more durable signals for connecting an ad click to a later conversion, and are central to cookieless tracking setups. A site must be built to capture and store the click ID at the moment of landing and pass it forward through to the conversion event, or the link is lost; a common implementation failure is stripping or not persisting the parameter across redirects, checkout flows, or subdomains.