Been using Syncthing quite happily on 2 Linux PCs and an android tablet here, just via my home router only. Lovely piece of work!
While watching Syncthing talking to itself in the console just now, I noticed an external address, https://relays.syncthing.net/endpoint , which when I browse to it, seems to be full of different relay IP addresses and the IDs of machines, shared folders, etc.
Not knowing too much about how ST works yet, please can anyone advise me whether my home network might be exposing private data with the outside world? I am ignorant, and curious
Where did you see that? The linked endpoint returns a list of relay server URLs. A relay URL includes the relay IP and ID, nothing more.
The overall question is partially answered in the FAQ:
Syncthing by default has relaying enabled. Relays are used when a direct connection is not possible. Anyone can run a public syncthing relay server (this is a different application, not a standard syncthing client). All data is E2E encrypted through the relay, so the relay doesn’t see much. The relay knows what devices are connected with each other and how much data they transfer, nothing more.
Folders, Folder names, device names, files, file metadata and file content are all E2E encrypted in transit no matter if a relay is involved or not.
