Regular expressions and languages

This is a tool for exploring the languages denoted by regular expressions.

To make it work, you'll need a browser that supports JavaScript.

Type a regular expression in one of the boxes (they all do the same thing) and hit return to see (part of) the language it describes.

Some things to try:

• a(a|b)*
• (a|b)*a(a|b)*
• ((a|b)(a|b))*
• (a|b)((a|b)(a|b))*
• b*ab*
• b*ab*ab*