Make your first call
Create a key in Settings → API, then:Start here
Authentication
Create a service account and API key, and understand which permissions each key really needs.
API Conventions
The rules every endpoint shares — envelope, errors, team scoping, pagination, CSV export, and ID types.
Contacts API
The most-used resource: list, create, merge, archive, and enrich contacts.
Liquid Syntax
Personalize SMS, email, and lessons — filters, snippets, and custom object queries.
Build an integration
Analytics
Identify contacts and track events from the browser with a client-safe key.
Webhooks
Receive events, and write contact fields back from your endpoint’s response.
Integrations
Zapier, SignWell, Okta, Cal.com, JotForm, and more.
Good to know
Not every endpoint works with an API key
Not every endpoint works with an API key
26 endpoints always return
403 for any API key, no matter how the service account is configured — all of Compliance, Roles and Senders, plus Teams writes, Org billing, and Webhook credentials. Service accounts cannot be granted admin, so these need a signed-in user. See Authentication.Pagination is not uniform
Pagination is not uniform
Only 8 list endpoints return a paginated envelope; 29 ignore
page entirely and return a flat array. Check the endpoint’s page before assuming page works — see Pagination.IDs are not all the same type
IDs are not all the same type
Most resources use an internal ID: a 24-character hex string. Links, Notes and Fields use integers, and Reports use string keys. Type your client’s ID fields accordingly.