Is the software for the server of https://snapcraft.io/ closed or open source?

I keep hearing different things from different people, some people are telling me that the reason people don't like snaps is because the software that runs the server for https://snapcraft.io/ is closed source and proprietary. Other people are telling that everything including the software for https://snapcraft.io/ is 100% open source and that everything in snaps is 100% open source. I don't know what or who to believe, so I wanted to post this question here and see if it can get resolved.