Interesting concept. As with all regex related online tools, it is important to test exhaustively before trusting it. Real-time character-by-character output w

Interesting concept. As with all regex related online tools, it is important to test exhaustively before trusting it. Real-time character-by-character output would be important. If you are working on a long regex expression real-time output can help you think like the FSA and see how it behaves. Here's an example of this tool failing: <a.*?>([^<]*)<\/a> http://gskinner.com/RegExr/?339m7 http://gskinner.com/RegExr/?339m7 or http://rubular.com/r/pCXZs0DnSS http://rubular.com/r/pCXZs0DnSS take your pick, same results. If you remove the "?" from the regex you'll get different results. One version selects all anchor tags individually and make a selection group of their contents and the other version ends-up selecting everything between the first opening anchor tag and the last closing anchor tag into the selection group except for "<" characters. The graph in Regexper does not show any difference between the two expressions even when any one of these forms is used: #<a.*>([^<]*)</a>#msi #<a.*>([^<]*)</a>#gsi /<a.*>([^<]*)<\/a>/msi /<a.*>([^<]*)</a>/gsi It looks like the flags are not being processed. Also, please change the textbox to a fixed width font. In addition to that, regex authoring tools, ultimately, are only useful if you can also enter some input text and see the result, preferably in real-time. Other than that, it's an interesting concept.