A leaderboard wouldn't be meaningful -- Client-side code isn't secure, and people could set scores to whatever they like. Or, just for fun, I played with the page a bit via dev tools, added in a script to automatically calculate the answer, put it in the input, and trigger the keyup event to run their submit function... worked great.

There is nothing wrong with client-side tools. I have a few on my site that get decent usage. But unless you put some security and validation on the server-side, any data coming back is not trustworthy.