If you're developing locally and need to use HTTPS for whatever, then this tool is hopefully useful to you.
I made it because there's a lot of bad info online about generating self-signed certificates. For instance, a lot of guides don't use the SAN list extension or show you how to create a proper certificate chain. Firefox doesn't allow a CA certificate to be used as an end certificate. Getting a working certificate can get pretty confusing, especially for newcomers to certificates or webdev.
Having a website for this also means the process of getting a certificate is the same, no matter if you're on a Unix-like OS or Windows.
A WebAssembly module built with C++ and Mbed TLS is used to create the keys and certificates. TypeScript and Preact is used for the UI.
mkcert does this really easily, one command and the CA is trusted in the system store, firefox, etc. and also has info on how to get it working with other stuff (e.g. mobile devices or node.js)
I'd say for someone who doesn't know certs, your site does not really make it easier, it's overwhelming, tons of options that people probably won't know what they mean.