Regular expressions are an essential part of any programmer’s toolkit. These are very useful kits for web developer to validate, match or replace text. To help user there are number of tools and resources are developed. The tools and resources like Greedliness / Laziness, Back referencing, Word boundaries, Named Groups, Word Boundaries, Atomic Groups, Recursion, Call Backs, Commenting, Regex helps to test regular expression in a different ways. If you would like to modify a htaccess file to make clean URLs, or some other advanced works as filtering RSS or other data. Some resources and tools given bellow which let you step forward to achieve good mastery over regex.