Conversion Tracking & Data
First-Party Cookies
By the AdFlint research team · Last reviewed July 2026
Set by the domain a visitor is actually on, readable only by that site, and used for sessions, carts, and measurement.
The browser stores them against your own domain, so they survive the third-party blocking that Safari and Firefox apply by default. Advertisers depend on them for session continuity and for holding click identifiers like the gclid. The limit people miss is lifespan: Safari's tracking prevention caps cookies written by JavaScript at seven days or less, which is why server-set cookies and server-side tagging exist.
First-Party Cookies compared with
The settings this gets confused with, and how to tell them apart.
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