Regex Tester
Test regular expressions with live matching, highlights, and capture groups. Runs entirely in your browser.
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What Are Regular Expressions (Regex) and Why Every Developer Needs Them
Regular expressions (regex or regexp) are powerful pattern-matching sequences used to search, validate, extract, and replace text in strings. They're supported in virtually every programming language (JavaScript, Python, Java, PHP, Go, Ruby, C#) and in tools like grep, sed, awk, VS Code search, and database queries.
Essential Regex Syntax Reference
.— Any single character (except newline)\d— Any digit (0—9), equivalent to[0-9]\w— Any word character (letters, digits, underscore)\s— Any whitespace (space, tab, newline)*— Zero or more of the preceding element+— One or more of the preceding element?— Zero or one (optional){n,m}— Between n and m occurrences^/$— Start / end of string (or line withmflag)[abc]— Character class: matches a, b, or c(group)— Capture group for extraction(?:group)— Non-capturing groupa|b— Alternation: matches a or b
Common Regex Patterns for Developers
\d+— Match one or more digits[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}— Email validation pattern^https?://— Match URLs starting with http:// or https://^\d{4}-\d{2}-\d{2}$— ISO date format (YYYY-MM-DD)^(?=.*[A-Z])(?=.*[a-z])(?=.*\d).{8,}$— Password strength (min 8 chars, mixed case + digit)\b\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\b— IPv4 address pattern
Regex Flags Explained
g(global) — Find all matches, not just the first onei(case-insensitive) — Match regardless of upper/lowercasem(multiline) —^and$match start/end of each line, not just the whole strings(dotAll) —.matches newline characters as well
Frequently Asked Questions
Enter a regular expression pattern and test string, and the tool uses JavaScript's RegExp engine to find matches in real time. Matches are highlighted in the text, and capture groups are extracted and displayed separately. All processing happens in your browser — no data is sent to any server.
This tool supports all standard JavaScript regex flags: g (global — find all matches), i (case-insensitive), m (multiline — ^ and $ match line boundaries), s (dotAll — dot matches newlines), u (Unicode), and y (sticky). You can combine multiple flags to customize matching behavior.
This tool uses JavaScript's regex engine, which follows ECMAScript standards. Most basic patterns (character classes, quantifiers, groups) work identically in Python, Java, C#, and PHP. However, advanced features like lookbehind, named groups, and Unicode properties may have syntax differences across languages.
Capture groups are portions of a regex pattern enclosed in parentheses (). They extract specific parts of a match. For example, (\d{4})-(\d{2})-(\d{2}) on "2024-01-15" captures "2024", "01", and "15" as separate groups. Use (?:...) for non-capturing groups when you need grouping without extraction.
Yes. All regex matching is performed entirely in your browser using JavaScript's built-in RegExp engine. Your patterns and test strings are never sent to any server or stored anywhere. You can safely test patterns against sensitive data like log entries, API responses, or personal information.