Security tools are the ones where using a website you do not trust defeats the purpose entirely. Everything in this category runs locally in your browser, so the password you generate or the string you hash is never transmitted anywhere and nothing is logged. Close the tab and it is gone. That is not a convenience feature here, it is the whole requirement.

One thing worth knowing if you are choosing a hash: MD5 and SHA-1 are broken for collision resistance and must not be used to verify that a file has not been tampered with, though they remain fine as fast non-security checksums. Use SHA-256 for anything that matters. And never store passwords with a plain hash of any kind, however modern, because they are designed to be fast and that is exactly what an attacker wants.