Regex Tester: Test Regular Expressions with Live Matching

Regular expressions are powerful pattern-matching tools, but they can be tricky to write and debug. Our Regex Tester provides instant visual feedback as you build patterns, showing matches in real-time with highlighted results and capture group details. Whether you’re validating email addresses, parsing log files, or extracting data from text, this tool helps you test and refine regex patterns quickly.

How to Use

1. Enter your regex pattern in the top input field (without delimiters)
2. Add sample text in the text area below to test your pattern against
3. Toggle flags as needed: g (global), i (case-insensitive), m (multiline), s (dotall), u (unicode)
4. View matches highlighted in the preview area with syntax coloring
5. Inspect capture groups for each match, including named groups if used
6. Copy all matches at once with the copy button for easy extraction
7. Reference the cheatsheet tab for syntax help on anchors, character classes, quantifiers, and more

Regex Flags

• g (global): Find all matches instead of stopping after the first match
• i (case-insensitive): Match both uppercase and lowercase letters (e.g., /hello/i matches “Hello”, “HELLO”, “hello”)
• m (multiline): Make ^ and $ match the start/end of each line, not just the entire string
• s (dotall): Allow . to match newline characters
• u (unicode): Enable full Unicode support for matching extended characters

Common Patterns

Email validation: ^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$ — Matches standard email formats

Phone numbers (US): \(?\d{3}\)?[-.\s]?\d{3}[-.\s]?\d{4} — Matches formats like (555) 123-4567, 555-123-4567

Hex color codes: #([a-fA-F0-9]{6}|[a-fA-F0-9]{3})\b — Matches #fff, #ffffff

Date (YYYY-MM-DD): \d{4}-\d{2}-\d{2} — Matches ISO date format

Extract numbers: \d+ — Finds all sequences of digits

Named capture groups: (?<year>\d{4})-(?<month>\d{2})-(?<day>\d{2}) — Extracts date parts with names

Frequently Asked Questions

Is this regex tester compatible with all programming languages? This tool uses JavaScript’s RegExp engine, which follows the ECMAScript standard. While most regex syntax is universal, some features vary by language. JavaScript uses (?<name>) syntax for named groups rather than Python’s (?P<name>).

Why isn’t my pattern matching? Common issues include: forgetting to enable the g flag for multiple matches, using ^ and $ without the m flag for multiline text, or special characters that need escaping with \. Check the cheatsheet tab for proper syntax.

What are capture groups and how do I use them? Capture groups use parentheses () to extract specific parts of a match. For example, (\d{3})-(\d{3})-(\d{4}) applied to “555-123-4567” creates three groups: “555”, “123”, and “4567”. Named groups like (?<area>\d{3}) make results easier to reference.

Can I test lookahead and lookbehind assertions? Yes, the tool supports positive lookahead (?=...), negative lookahead (?!...), positive lookbehind (?<=...), and negative lookbehind (?<!...).

How do I match special characters like dots or brackets? Escape special regex characters with a backslash: \. for literal dot, \[ and \] for brackets, \( and \) for parentheses, \\ for backslash.

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