Regex Tester

Real-time regex testing with match highlighting, capture groups display, and flag configuration. Supports JavaScript regex syntax.

Regular Expression
//g
Test String
Replacement (optional)

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Frequently Asked Questions

What regex flavor does this use?

This tool uses JavaScript's built-in RegExp engine, which supports most common regex features: character classes, quantifiers, anchors, groups, lookahead/lookbehind, and named groups.

What do the flags mean?

g (global) finds all matches. i (case insensitive) ignores case. m (multiline) makes ^ and $ match line starts/ends. s (dotAll) makes . match newlines.

How do I use capture groups?

Wrap parts of your pattern in parentheses to create capture groups: (\d+). Access them in replacements as $1, $2, etc. Named groups use (?<name>pattern) and are accessed as $<name>.

What is a lookahead?

A lookahead matches a position followed (or not followed) by a pattern without including it in the match. (?=pattern) is positive lookahead, (?!pattern) is negative.

About Regex Tester

Real-time regex testing with match highlighting, capture groups display, and flag configuration. Supports JavaScript regex syntax.

regexregular expressionpatterntestmatch