Regex Tester - Live Matching & Highlighting

How the Regex Tester Works

1. 01Enter your regular expression pattern in the pattern field
2. 02Set flags (global, case-insensitive, multiline) as needed
3. 03Paste or type test text in the input area
4. 04Matching text is highlighted in real time
5. 05Captured groups are displayed separately for inspection

Regular Expression Tips

Regular expressions (regex) are powerful patterns for matching and extracting text. Start simple: \d matches any digit, \w matches word characters, . matches any character. Use quantifiers: * (zero or more), + (one or more), ? (optional). Common patterns: email validation, phone numbers, and URL extraction. Always test with edge cases - regex that works on happy paths often fails on unexpected input.

When to Use a Regex Tester

Use this regex tester when building or debugging regular expressions for form validation, data parsing, search-and-replace, or log analysis. Interactive testing is much faster than embedding patterns in code.

Common Use Cases

• —Build and test email validation patterns before implementing in form code
• —Extract data from log files by matching timestamps, IP addresses, and error codes
• —Create search-and-replace patterns for bulk text transformations Diff Checker - Compare Text Side by Side
• —Validate input formats like phone numbers, postal codes, and credit card numbers
• —Parse structured text (CSV, log files, URLs) into components using capture groups

Expert Tips

• ✻Start simple and build complexity gradually - test each part of your pattern before combining them
• ✻Use non-capturing groups (?:...) when you need grouping for alternation but don't need to extract the match
• ✻Be cautious with greedy quantifiers like .* - use lazy versions .*? to match as little as possible and avoid unexpected results

Frequently Asked Questions

What is a regular expression?→

A regular expression is a pattern describing a set of strings. For example, \d{3}-\d{4} matches patterns like 123-4567. Regex is supported in virtually every programming language.

What do the flags g, i, m mean?→

g (global) finds all matches. i (case-insensitive) ignores case. m (multiline) makes ^ and $ match line boundaries. Combine them: gi finds all matches case-insensitively.

How do I match an email with regex?→

A simple pattern: [a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}. For production, validate basic format with regex then confirm via verification email.

Is my data private?→

Yes, all testing happens locally in your browser using JavaScript RegExp. No patterns or test strings are sent to any server.