Your data is transferred from you, through socket.io (trusted by millions) to the server where it gets hashed and returned to you.
It is also stored in something called 'localStorage', which saves your information so that when you refresh it's still there. If you want to remove stored data, you can click the 'Clear site data and refresh' button.
They are hashed on the Node.JS server, using the built-in crypto library. Node.JS is a popular server side language, so the results should be accurate.
This site was made by Lakshya Raj.