[hobr]

I find myself using Rubular (https://rubular.com/) quite often for experimenting with regular expressions.

[smoldesu]

I was working on a (FOSS) regex tester for desktop OSes using GTK and sourceview. Might pick the project back up soon, just gotta make sure that staying on GTK3 doesn't break my sourceview lib.

[greggman3]

I prefer this one though no Ruby (but maybe Ruby is the same as one of their supported langs?)

https://regex101.com

[lugoues]

Regext is one that I find quite helpful at times as well.

https://regexr.com/

[eduardosasso]

+1 I use Rubular quite a bit myself.