๐ Regex Tester
Regex Tester runs your pattern against sample text live, using JavaScript's ES2018+ regex engine โ lookaheads, lookbehinds, named groups and Unicode classes all work, while PCRE/Python-only syntax does not. Matches and capture groups are highlighted as you type, and nothing ever leaves your browser.
- PriceFree, no signup
- FlavorJavaScript ES2018+
- UploadNever โ local
- OutputHighlighted matches
Regex features in this tester
| Feature | Supported? | Note |
|---|---|---|
| Lookaheads & lookbehinds | Yes | ES2018+ engine |
| Named groups (? | Yes | Shown in the match list |
| Unicode classes \p{โฆ} | Yes | Pair with the u flag |
| PCRE / PHP-only syntax | No | JavaScript flavor only |
| Python-specific syntax | No | (?:โฆ) differences may bite |
| Catastrophic backtracking | Possible | A pathological pattern can hang the tab |
๐ Regex Pattern
๐ Test String
๐ Results
Highlighted Matches:
Regex Tester: Test regular expressions live
Regex Tester lets you test regular expressions live. Upload a regex pattern and get match results โ all processed locally in your browser, with no uploads and no sign-up.
Debug regex patterns
Debug regex patterns. This is one of the most common reasons people reach for Regex Tester โ and it handles the job in seconds, entirely in your browser.
Test matches against sample text
Test matches against sample text. This is one of the most common reasons people reach for Regex Tester โ and it handles the job in seconds, entirely in your browser.
Learn regex with live feedback
Learn regex with live feedback. This is one of the most common reasons people reach for Regex Tester โ and it handles the job in seconds, entirely in your browser.
Everything You Need in a Regex Tester
Powerful features that make Regex Tester fast, private, and free.
Instant Processing
Conversion and validation happen as you type.
Developer-Grade
Built for accurate, standards-compliant results.
100% Private
All processing is local โ no data is sent anywhere.
Copy & Export
One-click copy to clipboard for quick use.
Free Forever
No sign-up, no API keys, no limits.
Regex & JSON Support
Full regular expression and JSON validation built in.
How to Use
Enter your regex pattern
Type the regular expression you want to test in the Pattern field.
Add optional flags
Set flags like global, case-insensitive, or multiline to control how the pattern matches.
Paste the test text
Add the sample text you want to match against.
Review the matches
The tool highlights every match and shows captured groups, so you can verify the pattern before using it in code.
Detailed User Guide
Test regex patterns against sample text
The tester shows exactly what a regular expression matches, including capture groups, so you can debug a pattern before committing it to production code.
Flags change matching behavior
Case-insensitive (i), global (g), and multiline (m) flags alter how the pattern applies. Understanding them avoids subtle bugs in your expression.
Capture groups are highlighted
Parenthesized groups are shown separately, which is essential when you need to extract specific parts of a match, like a date or an ID.
Local and private
Your patterns and test data stay in the browser, so proprietary formats and sample data are never exposed.
Great for learning and debugging
Whether you are learning regex or troubleshooting a gnarly pattern, seeing matches highlighted live is far faster than guessing.
Common patterns to start from
Start with simple patterns like \d+ for numbers or [A-Za-z]+ for words, then build up. Seeing each small change reflected immediately helps you learn regex faster than reading a reference.
Watch out for catastrophic backtracking
Nested quantifiers โ patterns like (a+)+ matched against long input โ can freeze the engine with exponential backtracking. If a pattern hangs on a long string, look for a quantifier inside another quantifier and simplify it. Anchoring with ^ and $ and preferring specific character classes over lazy .* also keeps matching fast and predictable.
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