This was a tool that I originally designed to automatically no apps on Umbrel, modified to work on Citadel and also do automatic updated. However, it was a third (or 4th) parser of the app.yml format to maintain, and also wasn't very optimized.
With the release of app-cli, it has been rewritten as app-cli update, so this tool is not needed anymore.
A modified version of this tool, with its original purpose restored, now powers Upbrel: umbrel-apps-api.