If you have ever shipped a signup form, you know the moment. Somebody registers a username you really don't want on your leaderboard, and it's sitting there in the top ten by Friday.

So you add a word list. A week later they're back as sh1t, f.u.c.k or with a Greek letter swapped in, and when you tighten the list, somebody from Scunthorpe can't sign up anymore. (Written with AI help; every number here is checked against the source I link.)

And if you handed this problem to Google's Perspective API, there's a date in your calendar you may not know about: Jigsaw says the service runs until December 31, 2026, and its FAQ says access can't be extended past that.

So I went through the options developers actually reach for. Five are APIs, one is an npm package, one is on its way out. A few are free, and I'll say which. I'll also say where each one falls short, because nothing annoys me more than a "best tools" list where everything is perfect.

Let's start the list:

1.…