Regular expressions are like swiss knife which can do lot of work in small amount of code.
However knowing them deeply is very important to write code which is optimal.
I found below good websites for them while using and learning about them.
A very good website to have visual debugging for Regular expressions
https://www.debuggex.com/
Website to create and test regular expressions
http://regexr.com/
https://regex101.com/
A good website for Regular expressions tutorials
http://www.rexegg.com/
