RegExp 4+

This is the best regex app that I've used on MacOS/iOS/iPadOS. I've tried almost every single one. The iCloud sync and folder organization is terrific and better than any others. "Patterns" is wonderful but does none of this and you can't even open a new window without losing your old pattern, let alone creating a library of snippets to use. "RegEx Lab" saves them locally but does allow you to save multiples and import/export - I just wish it could save via iCloud.

That being said, there are a couple features that I consider almost a requirement that "RegExp" does not have:
1) Highlighting of the matches on your "test text" - it shows the matches in a window pane on the right along with line numbers, but it does not have line numbers on the test text pane so often it's difficult to determine what pieces from your text is actually matching.
2) Live updating - You have to click "Run" or use the shortcut "cmd r" to run the test. This can be a bit tedious, especially when paired up with the fact that there's no highlighting of the matches.

Developer: if you could implment those two features, I'd sing RegExp's praises to every colleague, student and heck, random person that I know

Note: For those who say you can't open two regular expressions at the same time, well you can. It's just a bit wonky. Click 'View' > "Show All Tabs" and it shows a tab preview like Safari, then click the " " and BAM a new tab with a new regular expression. It works perfectly, albeit not very user friendly. If the developer could just add a new tab shortcut or toolbar button, that would be terrific, but the main thing is that it works! EDIT: IT DOES HAVE A " " next to the tab, but you still need to click "Show Tab Bar" to see the tab bar and then the at the right of the single tab. YAY

I have been working on some projects requiring heavy regex usage. RegExp.app has been key to my success since I have been able to test and even improve the performance of my regular expressions. This app is very visual letting you see how the regex is processed via colored blocks that represent how pattern matching is applied.

The lead developer recently put in a small enhancement I requested which has allowed for removal vs substitution of values. This change was appreciated and works great.

The free version works nicely but the PRO version provides a ton of flexiblity.

I love this App and is the best regex app I have tried. Well worith the tiny price charged.