RegExr
My favorite is https://regex101.com/But I've found all of the following to be useful:http://regexone.com/http://www.regexpal.com/http://www.rexegg.com/http://regexr.com/https://www.debuggex.com/https://regexper.com/https://www.regular-expressions.info/http://www.cheatography.com/davechild/cheat-sheets/regular-e...http://eloquentjavascript.net/09_regexp.htmlhttp://www.smashingmagazine.com/2009/06/essential-guide-to-r...http://www.smashingmagazine.com/2009/05/introduction-to-adva...https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guid...http://codylindley.com/techpro/2013_05_14__javascript-regula...