First-party vs third-party, precisely
The distinction is about who sets the cookie or collects the data. A first-party cookie is set by the domain the user is actually visiting and is readable only by that site. A third-party cookie is set by an external domain embedded in the page, and was the mechanism behind cross-site tracking. First-party data — events, profiles, purchases collected on your own properties — is the durable version: it doesn't rely on anyone else's data-sharing relationship.
Third-party cookies aren't dead — but they're cornered
It is easy to overstate this. Google did not kill third-party cookies in Chrome: in April 2025 it reversed its plan to phase them out, and a further 2025 update retired much of the Privacy Sandbox ad stack while keeping a narrower set of features. But the direction of travel is clear: Safari and Firefox have blocked third-party cookies by default for years, and regulators treat non-essential cookies as needing consent. Relying on third-party tracking is building on ground that keeps shrinking.
| First-party data | Third-party cookies | |
|---|---|---|
| Set by | The site the user visits | An external embedded domain |
| Used for | Your own analytics and messaging | Cross-site tracking |
| Durability | Durable — you collect it | Shrinking — browsers block it |
| Who holds it | You | The third party |
First-party is not a compliance shortcut
First-party collection is more durable, but it is not automatically lawful. The regulator's position is that whether a cookie is first- or third-party is not the main consideration — non-essential cookies, like analytics or marketing, still need valid consent: freely given, specific, informed, and an unambiguous positive action. Pre-ticked boxes and "on" sliders don't count. Cookies strictly necessary for a service the user requested are exempt; everything else needs a yes. First-party data is the right foundation, but you still own the obligations that come with it.