RegExr

RegExr is gskinner's online tool for learning, building and testing regular expressions against JavaScript or PHP/PCRE engines, with results that update as you type. Hovering a match or any part of an expression explains what it does, a full reference sits beside the editor, and patterns can be saved, shared, checked against suites of tests or found in a rated community library. It is a dependable companion for design engineers writing validation, search or content transforms.