I have been fiddling around with Regular Expressions these days. As most people who ever tried it know that you can do about anything but it is at the same time nearly impossible.
Instead of making a test page, altering and refreshing minor changes all day I decided to look around a bit for a handy tool. There are a lot of them out there but I found a nice one.
The cool thing is you can easily switch between modes, modifiers and it automatically refreshed. The only minor point is that it is sometimes hard to see the difference between no match and an expression crash.
Check it out: Online regular expressions tester
Let me know if you found a better one!