RegExr is an online tool to learn, build, & test Regular Expressions.
This handy, interactive tool is a bit like Postman but for RegEx. You can create RegEx patterns and save them for easy retrieval later.
I also like the way you can start by making a list of example text strings you want your pattern to i) match and ii) not match before starting work on your RegEx pattern, adopting a sort-of “Test Driven RegEx” approach.