First-party data is information you collect directly from your own visitors and customers, for example through your website, forms, your store or a first-party cookie on your own domain. It is widely seen as the most reliable data source in online marketing.
How does first-party data work?
Anything that happens on your domain is yours to record: page views, clicks, form submissions and purchases, as well as UTM parameters and a click ID such as the gclid or fbclid from an ad click. A first-party cookie on your domain helps recognize a visitor across multiple page views.
This data becomes valuable for ad platforms when you send it back to them. Customer details like email or phone are hashed and sent along with conversions, for instance via Enhanced Conversions at Google or Advanced Matching at Meta.
Why does first-party data matter?
Third-party cookies are blocked by many browsers, Safari ITP shortens cookie lifetimes and ad blockers stop external scripts. Relying only on the ad platforms' own data means losing signals. First-party data is less exposed to all of this, and you own it. It typically improves Event Match Quality and makes your measurement more robust.
The GDPR still applies: data you collect yourself can generally only be used for advertising with consent. Our guide to GDPR-compliant tracking explains how to handle that properly.
Example
An agency works for a local contractor. A visitor arrives from a Meta ad with an fbclid, reads three pages and requests a quote. The fbclid, the landing page and the email from the form are all first-party data. Sent to Meta in hashed form, they let Meta reliably attribute the lead to the ad.
First-party data with LeadSignal
After consent, LeadSignal stores a first-party identity for each visitor and shows your leads in a person list with original source, click ID and landing page. UTM parameters are stored per session, and form fields are detected automatically and passed on, hashed, to Meta, Google or TikTok. Setup: one script, no developer.