Backups are made by a small local agent that watches your D2R save folder and uploads every changed file — characters (.d2s) and shared stash (.d2i).
Setting up the agent
Download the agent from the download page and run it — on the first launch a native dialog asks for a device token and your save folder, so there's no terminal or config file to edit. The full walkthrough, including the first-run security prompt, is in Download & set up the agent.
The agent is deliberately dumb: no parsing on your machine. It waits for the game to finish writing (saves are validated by their own header) and sends the raw bytes; all intelligence lives on the server.
Devices and tokens
Each machine gets its own named token, shown once at creation. Revoking a device immediately cuts its access; your snapshots stay.
Browser sessions
Below the device list, Devices also shows every browser you're signed in from — a short browser/OS summary, the IP address and when the session started. Your current one is marked this session.
If you see a session you don't recognise, or you signed in on a shared machine, click Sign out of every other device. It ends all browser sessions except the one you're using; the other machines simply have to sign in again. Changing your password does the same thing automatically.
Playing on multiple machines
By default the agent only sends your saves to the server — it never writes back to your local folder. If you play the same character on more than one machine, you can enable Two-way sync to automatically pull the latest save before you play. See Sync modes for details.
Uploads are never rejected
Every valid save is accepted and stored as a new snapshot, deduplicated by content hash. Losing a save is the one unforgivable sin.