In the era of the end of third-party cookies, everyone talks about first-party data — but there's an even more valuable category: zero-party data. The difference matters and is often confused. Here it is, clearly.
First-party data
First-party data is information you collect on your own site from a visitor's behavior — what they viewed, bought, where they came from. It's collected by observation (with consent) and is the basis of modern measurement. See cookieless measurement and first-party data.
Zero-party data
Zero-party data is information the customer gives you themselves, deliberately and proactively — preferences in a profile, answers in a survey, a declared intent ("I'm looking for a gift"). It's not inferred from behavior but directly shared.
Why both are valuable
- Independence from third-party cookies. Both belong to you and the customer's consent, not an ad network.
- Zero-party is precise. What the customer tells you, you don't have to guess — higher quality for personalization.
- First-party is voluminous. It's created on every visit, so there's a lot of it.
How to measure and use them
You collect first-party data reliably via server-side tracking — data flows through your domain and you control it. Zero-party data you get from forms, quizzes and profiles, and connect to measurement (e.g. a hashed email for better matching — see what hashing is). Together they form a foundation that outlasts the end of third-party cookies.
Summary
First-party data you collect from behavior, zero-party the customer gives you themselves. Both belong to you and consent, not an ad network — and both are the way forward after the end of third-party cookies. Server-side tracking is the tool to collect and use them reliably. More in the complete guide.