Question 1

What is a regex debugger?

Accepted Answer

A regex debugger (or regex visualizer) lets you see exactly how a regular expression matches a given test string. It highlights every match, shows the position of each capture group, and breaks down the regex pattern token by token so you can understand why it matches (or why it doesn't). It is invaluable for fixing patterns that behave unexpectedly.

Question 2

Which regex flags are supported?

Accepted Answer

All standard JavaScript regex flags are supported: g (global — find all matches), i (case-insensitive), m (multiline — ^ and $ match line boundaries), s (dotAll — . matches newlines), u (unicode), and y (sticky). Toggle them with the flag chips above the test area.

Question 3

Is my text or regex uploaded to a server?

Accepted Answer

No. This regex debugger runs entirely in your browser using the built-in JavaScript RegExp engine. Neither your pattern nor your test string ever leaves your device, so it is safe to debug patterns against proprietary or sensitive data.

Question 4

Why does my regex work here but not in my language?

Accepted Answer

Different programming languages use different regex engines with subtly different syntax and behavior. This tool uses the JavaScript (ECMAScript) regex engine. If your regex uses features like lookbehind (?<=...), named groups (?P<name>...) or possessive quantifiers, they may behave differently in Python, PCRE, Go RE2 or Java. Always test in your target environment.