Q. Which regex engine?
JavaScript's native RegExp. Standard ECMAScript syntax — Python/Perl variants (lookbehind etc.) may differ slightly.
Q. What do the flags mean?
g (global), i (ignore case), m (multiline), s (dotall), u (unicode). Toggle them live.
Q. How are capture groups shown?
Each ( ) group gets a distinct color in the match highlight, with index/name and value listed.
Q. Does it support replace mode?
Yes — substitute matches with strings using $1/$2 back-references or named groups $<name>.
Q. Where can I learn regex?
MDN RegExp docs, regex101.com, regexr.com — this tool is for fast testing.
Q. Is my data sent to a server?
No — evaluation runs locally, safe for sensitive patterns (email, phone).
