Regex Coach you can experiment with (Perl-compatible)
regular expressions interactively. It shows whether a
regular expression matches a particular target string.
It can also show which parts of the target string
correspond to captured register groups or to arbitrary
parts of the regular expression. It can "walk" through
the target string one match at a time. It can simulate
Perl's split and s/// (substitution) operators. It can
single-step through the matching process as performed by
the regex engine. Everything happens in "real time": as
soon as you make a change somewhere in the application
all other parts are instantly updated. Further, The
Regex Coach tries to describe the regular expression in
plain English and it can show a graphical representation
of the regular expression's parse tree.