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This walks the whole path once: create the account, grab a key, identify a contact, and read it back. Everything below runs against https://api.userkit.dev.

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1. Create your account

Sign up at app.userkit.dev. Sign-up creates the user, the organization, your owner membership, both environments and their publishable keys in a single transaction, then drops you into the panel.
Every organization is born with a live and a test environment. What separates them is the key you present, never a parameter — start in test and nothing you do here shows up in production’s numbers.

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2. Mint an API key

In the panel, Settings → API keys, create a key in the test environment. A key is born inside one environment and never leaves it; the environment is recorded in the prefix itself (uk_sk_test_…).
The key’s value is shown exactly once. Only its SHA-256 hash is stored, so a lost key is replaced, never recovered.

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3. Check the key

The first call every integrator makes. What comes back is the environment the key belongs to — nothing you send can name a different one.
Response

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4. Identify a contact

Now the customer plane. Send whatever identities your backend knows; at least one of external_id, email or anonymous_id is required.
Response — 201
Call it again with the same external_id and you get 200 with "created": false — identify is create-or-update, not create.
email_verified stays false until an actual link is clicked. Passing an email to the API records an attribute; it does not prove one.

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5. Read it back

The detail read adds the contact’s identity edges — the values that resolve to it:
Try the same id with a live key and you get 404. That is environment isolation working: the key’s environment scopes the read, and the 404 does not reveal whether the row exists somewhere else.

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Where to go next

Contacts

Identity edges, attribution and how merges work.

Choosing an auth mode

Hosted or federated — decide before you wire the front end.

Environments

What live and test actually separate.

Roles and permissions

Give your teammates less than everything.