What is Expressions? It’s an easy-to-use and nice-looking regex tester for macOS. Live preview, library, and regex manual enclosed in a beautiful user interface.

Just type your text and pattern to test it. All the changes are being updated while you're typing text or pattern. The app highlights the syntax, so the pattern is easy-to-read and to 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 the button in the top-right. You will get the reference sheet.

You can open the app in beautiful full-screen mode, perfect when you want to focus or demonstrate regular expressions to others.