Regulator is a full-featured Windows-based tool that makes it easy to build and test regular expressions. There is excellent support for them in the .NET Framework and they have been around for a long time in UNIX based utilities like sed and awk. Regular expressions are used to define patterns in strings based on characters, frequency, and character order. They are most commonly used as a means to validate user input or as a way to find a string of characters inside a larger string—for instance, when looking for a URL or e-mail address on a Web page. Regulator allows you to enter a regular expression and some input against which you would be running this expression. This way you can see how the regular expression will act and what kind of matches it will return before implementing it in your application. The ability to write and test regular expressions in a separate application like this is much easier than trying to work with them in your app. One of the best features in Regulator is the ability to search the online regular expressions library at regexlib.com. For example, if you enter the string "phone" in the search box, you will find more than 20 different regular expressions that will match various phone numbers, including expressions for UK, Australian, and many other phone numbers.