I found need earlier today for an easy way to quickly trigger a rescan from the command-line, and found that there really isn't one, so I've written a tool to do so, and it kind of evolved a bit from there with the intent of eventually being able to not need the web GUI at all.
Source code can be found here;
Currently, it's pretty rudimentary (it only supports rescanning folders and overriding remote changes to send-only folders, and doesn't have great error handling), but it works well enough that I felt comfortable putting it on Github so that other people can make use of it if they want.
Initial setup is dead simple, just run:
stcli.py setup /path/to/your/syncthing/config.xml
and it will pull out the info it needs into it's own config file in
I'm planning on adding a majority of the other currently used REST API calls as time permits (there are a handful that I plan on not adding for various reasons, see the README file in the repository for info).