How can users be sure that their inputs are not being saved somewhere on the backend? If I paste a bunch of content into these forms, and it inadvertently has some sensitive data in it, such as a credential or key of some kind, how do I know that isn't a data breech?

I would assume it goes without saying to be careful and never use credentials or keys in an online tool that way, mine or otherwise. I don't save data but its something I'll work on to ensure.

Can't imagine what kind of stuff ChatGPT has on us too :D

If you don’t already know the answer to that question (e.g. monitoring network calls in your browser), why would you trust an answer from the same service providing the tools?

This is why web tools are typically a last resort for me, after all local options have been exhausted (usually, I can't get them working because an old binary is broken, building the code is borked, the local tool silently fails while offering no feedback, etc).

How can you ever be sure of that on any website that you don't fully host yourself?