# How identity works

This is the map, not the manual. By the end you'll be able to answer three questions: which tier you are, whether cross-platform stitching applies to you, and the one rule that makes it work.

Source: https://cross-deck.com/university/how-identity-works/
Verified Crossdeck University lesson — prose plus real, runnable code.

## Crossdeck binds a person to the most durable anchor you provide

Everything about identity follows from one idea: Crossdeck attaches a person to the most durable anchor your setup gives it — an anonymous handle, a Stripe customer, or your own app's user ID. The more durable the anchor, the more Crossdeck can do. So where you sit isn't a setting you pick; it's a consequence of what your app already has.

## Find yourself on the ladder

There are three tiers, climbing from least to most durable. Most apps know their tier in one read:

## The same UID on web and mobile is the same human

On Tier 3, the whole mechanism is this: you hand Crossdeck the same UID on web and on mobile. The web subscription attaches to that UID; the mobile install's anonymous handle aliases into it — so Pro resolves on the phone too. You assert the identity; Crossdeck doesn't guess, fingerprint, or match on email.

And the one rule that makes it work, the one to never get wrong:

## You know your tier — now you know what to do

If you're Tier 1 or Tier 2, you're done — cross-platform identity doesn't apply to you, and that's fine. If you're Tier 3 with real accounts on web and mobile, there's exactly one thing to do: call identify() with the same UID on both platforms. The next lesson wires that to your auth provider.

one person, two platforms
 On Tier 3, user_847 is one record — web subscription attached, mobile handle aliased in, Pro live on both. The UID is the passport.