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How to Test Regular Expressions
The Regex Tester lets you write a pattern, supply test strings, and see matches highlighted in real time — with capture group details and match indices.
- Enter your regex pattern in the pattern field and select flags (global, case-insensitive, multiline).
- Type or paste test strings in the input area.
- View highlighted matches, capture groups, and match details instantly.
Understanding Regular Expressions
Regular expressions (regex) are patterns that describe sets of strings. They are used in search, validation, data extraction, and text transformation across virtually every programming language. Common constructs include character classes ([a-z]), quantifiers (+, *, ?), anchors (^ and $), and groups ((...)). Mastering regex is a fundamental developer skill.
Why Use Our Regex Tester?
- Live highlighting — matches are highlighted as you type the pattern.
- Capture groups — see named and numbered groups with their values.
- Flag toggles — easily switch between global, case-insensitive, and multiline modes.
- JavaScript engine — uses the exact same regex engine as Node.js and browsers.
Frequently Asked Questions
Which regex flavor does this use?
JavaScript (ECMAScript). Patterns compatible with JS will work here. PCRE-only features like lookbehind (now supported in modern JS) and possessive quantifiers may vary.
Can I test regex for other languages?
JavaScript regex is very close to Python, Java, and Go regex for common patterns. Language-specific extensions may differ.
What do the flags mean?
g (global) finds all matches, i (case-insensitive) ignores case, m (multiline) makes ^ and $ match line boundaries instead of string boundaries, s (dotAll) makes . match newlines.
Is my test data private?
Yes. Everything runs in your browser. No patterns or test strings are sent to any server.