A super simple app for playing with and testing regular expressions. Expressions is probably the best looking regex app with a beautiful minimalistic UI, fullscreen support, automatic dark and light modes, and an editor that gives you full regex syntax highlighting and a live preview of your expression's results. You can choose between highlighting entire matches or just a single group within your match and easily switch between matched groups with a keyboard shortcut of menubar item.

Expressions allows to play with regular expressions*. Just type your pattern and some text to test it. All the changes are updated while you're typing text or pattern. App highlights the syntax, so the pattern is easy-to-read and modify. If you use subexpressions (groups), you can highlight them by pressing cmd+shift+] (or [ – for decreasing the highlighted group number).

If you don't remember the regex syntax, just press cmd+r or click button in the top-right. You will get the reference sheet, so you don't have to remember everything.

The user interface is very minimalistic and non-distractive. By default the color is the same as your menubar, but you can always switch to dark or light mode (see: Preferences). You can also open app in beautiful full screen mode which is perfect when you want to focus or to demonstrate regular expressions to other people.

* Expressions uses ICU regular expression standard. More information you will find here: https://developer.apple.com/reference/foundation/nsregularexpression