A simple and easy to use all-in-one solution which helps a developer in all aspects of working with regular expressions - Learning, Building, Testing and Organizing.

Features:

Builder
- Building a regular expression is as easy as browsing the built-in regular expressions language reference, double clicking on the language elements to insert them into your regular expression.
- Paste your regular expression from Java Code, convert it into a regular expression (all \\'s to \'s converted automatically), modify and/or test it, then automatically convert it back to a java string.
Tester
- Uses java.util.regex API for robust regular expressions matching
- Syntax Validation
- Matches the regex against an input text and shows match results in the form of a tree, with matches at the first level with their matched groups at the second level.
- Match results show individual groups matched with exact position and sub-sequence.
- Clicking on a match highlights the sub-sequence in the input text window.
- All regular expressions compilation options supported -Multiline, Dotall mode, etc.
Complete Regular Expressions Language Reference
- No need to leave Netbeans to refer language reference for regular expressions
- Divided into intuitive categories- Characters, Character Classes, Grouping Constructs, Substitutions, various types of Quantifiers, etc.
- All the language constructs described in java.util.regex.Pattern javadoc are included.
- Click on a language element to see it's description in the pane below.
- Very helpful for newbies and learners. Gets you up to speed quickly.

Usage: To open the regular expressions plugin window, go to Tools > Regular Expressions Plugin.

Demo Video: I've made a small video showcasing the features of the plugin by showing how to build and test a regular expression for checking email addresses: Watch Video

regex.dev.java.net: project release sources, mailing lists, issue tracker, etc
wiki.netbeans.org/Regex: Documentation, information about development sources, other useful links, etc.