Unified ID 2.0 (UID2)

Unified ID 2.0 (UID2) is an open-source identity framework, originally developed by The Trade Desk, that turns a user's email address or phone number into a hashed, encrypted identifier usable for ad targeting and measurement, without relying on a browser's third-party cookie.

How the identifier is built#

A publisher or advertiser collects a user's email (typically through a login or sign-up, with consent), then that email is hashed and encrypted using the UID2 protocol before it's ever shared with an ad tech vendor. The resulting token can be matched across participating publishers and demand-side platforms without any of them seeing the underlying email in the clear. The encryption is refreshed on a rotating basis, and a user can opt out or reset their identifier through participating opt-out tools, which is meant to give more direct control than a cookie ever offered.

Because UID2 is built around a directly-collected identifier rather than passive browser tracking, it depends heavily on first-party data collection at the point of login or registration. A publisher without a reliable sign-in flow has a much harder time generating UID2 coverage than one with an established registration wall or newsletter sign-up.

Why it exists#

UID2 was built as an industry-wide response to the same problem cookieless targeting methods generally address: third-party cookies don't work reliably in Safari or Firefox and are increasingly restricted or blocked across the open web, which broke a lot of the real-time bidding targeting and attribution logic the industry had built around them. Rather than each platform building its own closed identity graph, UID2 is published as an open standard specifically so multiple vendors, not just The Trade Desk, can adopt and interoperate with it, which is different from a walled-garden ID that only works inside one company's ecosystem.

Where it fits and where it doesn't#

UID2 depends on a user having taken some action, logging in, subscribing, or checking out, that gave a publisher or advertiser their email in the first place. That makes it strong for retail, subscription, and login-gated media, and weaker for the kind of anonymous, drive-by traffic that dominates a lot of native advertising and open-web resold inventory. Native buyers evaluating identity solutions generally need to weigh how much of their actual traffic is logged-in versus anonymous before assuming UID2 coverage will match what cookies used to deliver.

If you're trying to figure out which networks and advertisers are actually adapting well to a lower-cookie environment, rather than reading vendor claims, comparing live creative volume and vertical mix across networks in OpenAdLibrary's ad intelligence index is a more direct signal than any single identity vendor's coverage numbers.

What advertisers should actually check#

Before assuming UID2 or a similar identifier will preserve your targeting and measurement, look at how much of your actual audience logs in or otherwise shares an email versus arrives anonymously. A subscription publisher or an ecommerce brand with a loyalty program will typically see solid coverage; a purely anonymous top-of-funnel native campaign may see much less, which is worth modeling before you rebuild a measurement stack around any single identifier.