RegEx Builder is a small utility to help you build regular expressions. Especially useful for those, like me, who don’t use regular expressions everyday, and therefore, don’t always remember all the details.RegEx Builder does not eat too much memory, it is easy to install and has a simple but efficient interface. What is a regular expression? A regular expression is a string that is used to describe or match a set of strings, according to certain syntax rules. Requires Microsoft .NET Framework 2.0.