Regex Tester

Test regular expressions against sample text with real-time match highlighting and capture group extraction.

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Pattern

Test String

Matches

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Regular Expression Syntax Quick Reference

Pattern	Matches	Example
\d	Any digit 0-9	\d{3} → 123
\w	Word character [a-zA-Z0-9_]	\w+ → hello
\s	Whitespace	\s+ → spaces/tabs
.	Any character except newline	.+ → anything
[abc]	Character class	[aeiou] → vowels
^...$	Start/end anchors	^\d+$ → digits only
(x\|y)	Alternation	(cat\|dog) → cat or dog
x{n,m}	Quantifier n to m times	\d{2,4} → 12, 123, 1234

Common Flags

g — Global: find all matches, not just the first
i — Case-insensitive matching
m — Multiline: ^ and $ match line boundaries
s — Dotall: . matches newlines too

Frequently Asked Questions

What regex flavor does this use?

JavaScript (ECMAScript). Most patterns work the same in Python, Java, and PHP, but lookbehind support varies by engine.

Can I test replacement patterns?

This tool focuses on matching. For search-and-replace, use your code editor or a dedicated tool like sed/awk.

Related Calculators

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How to Use This Regex Tester

Enter a regular expression pattern and test string. The tester highlights matches, shows capture groups, and explains each part of your pattern in plain language.

Formula & How It Works

Common patterns: . (any char), * (0+), + (1+), ? (0-1), \d (digit), \w (word char), \s (whitespace), [abc] (char class), ^ (start), $ (end), (group), {n,m} (repeat).

Calculation Example

Pattern: ^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$ matches email addresses like user@example.com.

Expert Tips

Build regex incrementally — start simple and add complexity. Use non-greedy quantifiers (*? +?) to avoid over-matching. Test with edge cases. In production, prefer established libraries for email/URL validation over custom regex.