Expressions lets you play with regular expressions (regex). 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. Note:Expressions uses ICU regular expression standard. More information here.

Features

• Totally minimalist, unobtrusive user interface
• Dark and light modes
• Pattern syntax highlighting
• Beautiful full-screen view
• Pattern and text-group highlighting
• Support for switching between pattern groups by pressing Cmd+Shift (and Cmd+Shift++)
• Copied patterns can be escaped so you can paste them directly into your code--and the other way round, of course (see Edit menu)
• The "Allow whitespaces and comments" option lets you break patterns into parts, which makes editing much simpler (see Preferences)