Test regular expressions with live match highlighting and match details.
Frequently Asked Questions
This tool uses JavaScript (ECMAScript) regular expressions, which is the regex engine built into all modern browsers. It supports features like lookahead, lookbehind (in modern browsers), character classes, quantifiers, and named groups.
Common flags: g (global - find all matches), i (case-insensitive), m (multiline - ^ and $ match line boundaries), s (dotAll - . matches newlines), u (unicode), and d (hasIndices).
Regex patterns with nested quantifiers (like (a+)+ or (a|b)*c) can cause catastrophic backtracking. If a pattern takes too long, simplify it by using atomic groups or possessive quantifiers where possible.
The highlighted view shows all matches. The match list shows up to 50 matches with their index positions. If there are more than 50 matches, the count is shown.