On your device.
There is no account to create and no server to log into. Your library, listening history, bookmarks, and preferences live on the device you listen on.
That is a deliberate design choice, not a missing feature. Cranesoft does not sell your data and does not build advertising profiles.
Two things are opt-in and under your control:
- Hardcover.app sync — if you link a book, Crane talks to Hardcover only to sync what you asked it to.
- Diagnostic feedback — if you choose to send a report, it carries the details needed to investigate that issue.
Neither is on unless you turn it on.