[nodata]

Why would you need to be sure of that?

[stephenr]

Because they can say "hey look at our code here" when in fact they're running something else entirely.

[danbruc]

But that does not matter if you trust your client and everything gets encrypted locally. That's the entire point of client-side encryption, not having to trust the server. Just review and then compile the client. And just self-hosting the server will not make you any saver because the client may be rogue and send your data to anyone.