The MonogameExtended animation guide (linked below) points to using SpriteFactory. It didn’t seem to load textures when run locally and crashes randomly (Win10/64). It was also unclear if the .sf files exported will be supported or reflect an older version of SpriteSheet (class structure seemed a bit different). Should update the docs if it is no longer supported. When I tried building from source it broke with code 9009 (from MGCB).
I have my own Sprite tool but I stumbled upon SpriteFactory when I was looking at the best way to import the sprites into Monogame. I didn’t want to re-invent the wheel but it’s also unclear if mimicking the SpriteFactory json is the best way forward.