Regex Tester

By the FastFreeTools Editorial Team · Last reviewed: May 2026 · See our Editorial Policy for methodology, sourcing, and disclaimers.

Test and debug regular expressions with live match highlighting. View capture groups and test with all standard flags.

About this tool

Regular expressions are powerful pattern-matching tools used in virtually every programming language for text search, validation, and transformation. Our Regex Tester provides live match highlighting as you type, displays capture groups for each match, supports all standard flags (global, case-insensitive, multiline, dotAll, unicode), and shows match details including index positions. The instant visual feedback makes it dramatically faster to develop and debug regex patterns compared to testing in code. Developers use this for building validation patterns, parsing log files, extracting data from text, and creating search-and-replace rules.

How to use Regex Tester

Enter your regular expression in the pattern field.
Select the flags you need (global, case-insensitive, etc.).
Enter test text in the input area.
View highlighted matches and capture groups in real-time.

Tips & best practices

Start simple and build complexity gradually.
Use the global (g) flag to find all matches, not just the first.
Named capture groups (?<name>...) make complex patterns more readable.
Test edge cases: empty strings, special characters, and multiline input.

Common use cases

Building email, phone, and URL validation patterns.
Creating search patterns for log file analysis.
Developing text extraction and transformation rules.
Learning and teaching regular expression syntax.

Privacy

This tool runs entirely in your browser. We do not upload, store, log, or process your input on any server. Open your browser's DevTools Network tab to verify — there is no outbound request with your data. See our Privacy Policy for details.

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