RegExr

RegExr is an online tool designed for learning, building, and testing regular expressions in real time. Created by gskinner.com, it supports both JavaScript and PHP/PCRE regular expression flavors, making it suitable for front-end and back-end developers alike. The interface provides a three-panel layout where users type an expression in the left panel, enter test text in the center, and see match highlights update instantly as they type. Hovering over a matched portion or the expression itself shows detailed explanation of what each part of the pattern does. Additional features include a full regex reference sidebar with syntax cheatsheets, community pattern library with search and rating, unit tests for validating expressions against expected matches and non-matches, and tools for replace operations, detailed capture group inspection, and plain-English expression explanation.