[btown]

Highly recommend regex101 to anyone reading this. Multiple language support, colored highlights based on which group matched, a full-fledged debugger that steps through every character tested, and substitution with group references. That said, OP's solution has a much simpler interface, and if you like that kind of thing for focus, it seems like it's a great little app!

[obihill]

This has a simpler interface, yes. But, it took me a while to get comfortable with regular expressions, so the explanations of what was going on was like a built-in tutor, and apps like this definitely need this to be useful to learners.