What is a GCLID?

A GCLID, or Google Click Identifier, is a unique code Google Ads appends to your landing page URL when someone clicks your ad, for example ?gclid=Cj0KC.... It lets Google connect that specific click to whatever the visitor does next, including a purchase reported later.

Why it matters

The GCLID is what makes offline and server-side conversion tracking possible for Google Ads. When a sale happens hours or days after the click, or completes somewhere the pixel cannot see, you can still report it to Google by sending the conversion back with the original GCLID attached. Google matches it to the click and credits the right campaign.

Related identifiers

On iOS and other privacy-restricted surfaces, Google may use GBRAID and WBRAID instead of a GCLID. Meta has the fbclid, Microsoft the msclkid, and TikTok the ttclid. They all serve the same purpose: a durable link between a click and a conversion.

Trakt captures the GCLID and its equivalents first-party on your domain, so the click survives to be matched even when the browser drops its cookies.