[huhtenberg]

Good stuff. It is the first Show HN site that I actually bookmarked for later. It is well-done and it is interesting.

A couple of things though. Requiring an email address upfront means that I will feed you a @mailinator.com one. Let people play with the site a bit, and then require creating an account if they want to save the progress... or something along these lines.

Second, a confirmation email appears to include a numerical user ID. This inadvertently discloses the number of users you have to anyone who signs up. May want to fix that.