First-party vs. third-party cookies
A first-party cookie is set by your own domain and still works. A third-party cookie is set by another domain and is effectively history: blocked by default in Safari and Firefox for years, while Chrome went through deprecation, reversal and Privacy Sandbox. The practical consequence for 2026: measurement moves to first-party data, server-side and modeled conversions.
Who sets the cookie: the domain the user is on (first-party, works) or a third domain (third-party, widely blocked).
1P cookie
First-party cookieA cookie set by the domain the user is visiting (yours). Unlike third-party cookies, it is less affected by browser restrictions and has a longer lifespan — especially when set server-side, on your own domain.
It's the base of any measurement that will still work in two years. Combined with server-side tagging and a custom domain, its lifetime improves.
3P cookie
Third-party cookieA cookie set by a domain other than the one being visited, historically used for cross-site tracking and retargeting. Google abandoned its plan to remove them from Chrome in 2024 (confirmed in 2025), but their effectiveness is declining anyway: Safari and Firefox block them, ITP shortens them, and opt-outs are rising.
You don't choose it — you inventory it. Any remaining dependency is technical debt: find it and move it to first-party or to the server.
This comparison is part of the Atlas — Websem's reference of AI search, Google Ads, tracking and chatbot terms. 129 terms, each with its own definition.