How sync works

Every device keeps a connection open to the server, so a change on one device reaches the others in real time.

Figure — a change on the PC is encrypted, broadcast by the server, and decrypted on the phone

1. A connection stays open. Every device keeps a WebSocket connection to the server.
2. A change is encrypted and pushed. The plugin sees the changed file, encrypts it on the device, and sends the new version to the server.
3. The server broadcasts it. The other devices of the vault are told that something changed.
4. They pull and decrypt it. Each device fetches the new version and decrypts it on the device.

The vault password never leaves your devices, so the server only ever passes on ciphertext it cannot read.

A phone does not sync in the background, so reopening Obsidian often means catching up on a batch of changes. Courier brings the note you have open, and the ones you opened recently, up to date first and catches up on the rest behind them — so opening Obsidian on a phone never feels like waiting for sync.