I had a hard time with complex regex until I started using them more in vim - the ability to see what your regex matches as you work is really helpful. Of course, this is even better now with sites like regexr and regex101
Regex101 is always open when I'm doing regexes, what a great tool. Occasionally I use sites that build the graph so you can visualize the matching behaviour.
There are even tools to generate matching text from a regex pattern. Rust's Proptest (property-based testing) library uses this pattern to generate minimal failing counterexamples from a regex pattern. The tooling around Regex can be pretty awesome.
