Flags modify match behavior: "g" performs global matching across all occurrences, "i" makes searches case-insensitive, "m" enables multiline anchors (^ and $ match line starts and ends), "s" allows the dot (.) to match newlines, and "u" enables full Unicode support.
DEVELOPER & CODE·Client-Side (100% Private)
Regex Tester & Explainer
Test, validate, and debug regular expressions with real-time match highlighting, capture groups, cheat sheet, syntax explainer, and substitution preview.
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Data entered into this tool is processed 100% locally within your browser. Nothing is ever sent to or logged on any server.
FREQUENTLY ASKED QUESTIONS
Frequently Asked Questions about Regex Tester & Explainer
Quick answers to common questions about usage, conversion rules, privacy guarantees, and best practices.
How do regular expression flags (g, i, m, s, u) work?
Can I test regex replacement patterns and capture groups?
Yes. You can test substitution rules using numbered backreferences ($1, $2) or named capture groups ($<name>) with live replacement previews.
How do lookahead and lookbehind assertions work in JavaScript regex?
Lookaheads (?=...) and negative lookaheads (?!...) assert what follows without consuming characters. Lookbehinds (?<=...) and negative lookbehinds (?<!...) assert what precedes the match position, enabling precise contextual validations.
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