What is Regex Tester?
Regex Tester lets you run a regular expression against sample text and inspect matches, capture groups, flags, and replacements in real time. It is useful for validation, parsing, search, data cleaning, and debugging patterns before they go into code.
Why Use This Regex Tester?
Testing regular expressions directly in your code editor means rerunning the whole program to see results. This tester gives you instant visual feedback —matches highlight as you type, capture groups are listed, and you can test a replacement string before committing it to code. Everything runs in the browser with no data sent to a server.
- Live matching: Results update on every keystroke —no submit button needed.
- Capture group inspection: See each group's value individually, not just the full match.
- Flag toggles: Switch global, multiline, case-insensitive, and dotAll with a click.
- Replace preview: Test your replacement string before using it in production code.
How to Use Regex Tester
- Enter the regular expression pattern you want to test.
- Paste the sample text the pattern should run against.
- Toggle flags such as global, multiline, or case-insensitive as needed.
- Review matches, groups, and replacement output before using the pattern.
Quick Guides
Regex Patterns Quick Reference helps you look up common expressions, flags, and escaping rules before testing a pattern live.
Understand Regular Expressions ▾
Example
Common Use Cases
- Debug JavaScript regular expressions against real sample text
- Inspect capture groups and replacement output before writing code
- Test validation patterns for forms, logs, or parsing tasks
- Share clear regex examples during documentation or onboarding
Why Use This Tool
- Useful for validation rules, parsing, and search patterns.
- Lets you test flags, groups, and replace mode without opening DevTools.
- Runs locally so logs and sample text stay in the browser.
Frequently Asked Questions
This tool uses the JavaScript RegExp engine built into your browser. JavaScript regex supports most standard features —character classes, quantifiers, groups, lookaheads, lookbehinds —but differs from other flavors (PCRE, Python, Java) in some edge cases like named backreferences and certain Unicode properties.
g (global) finds all matches instead of stopping at the first. i makes matching case-insensitive. m makes ^ and $ match the start/end of each line rather than the whole string. s (dotAll) makes . match newline characters too.
Escape it with a backslash: \. matches a literal dot, \( matches a literal opening parenthesis. Without the backslash, . matches any character and ( starts a capture group.
A capture group is a part of the pattern wrapped in parentheses (...) . Whatever it matches is extracted separately and accessible as $1 , $2 , etc. in replace operations, or as array elements in code. Use (?:...) for a non-capturing group when you want grouping without extraction.