No cookies, no login, no account. Just by loading this page, a website already knows more about you than you'd guess. The checks below run automatically and never leave your browser. There's one optional check further down that contacts two outside services to show you what they'd see.
Want the deep version of this, checked against real data from other visitors? The EFF's Cover Your Tracks does that.
Plot the integers in a spiral and mark the primes, and they don't fall randomly. They cluster along diagonal lines more than chance would predict. Nobody's turned that into a shortcut for factoring, but it's a genuinely pretty pattern. This runs a Sieve of Eratosthenes client-side in your browser and walks the spiral live.