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Pattern notes
Pattern analysis appears after you enter a regular expression
What is Regex Tester?
An online JavaScript regex tester for checking patterns, flags, capture groups, replacements, and common expressions with live highlighting.
Key Features
- Live regex match highlighting
- Capture group and named group display
- Find and replace testing
- Common regex presets
- JavaScript regex flags
- Pattern explanation hints
Common Use Cases
- Debug JavaScript regular expressions
- Test extraction patterns before coding
- Check capture groups and replacements
- Learn common regex patterns
Example workflow
- Enter the pattern and flags you expect to use in production.
- Add positive examples that should match and negative examples that should not match.
- Inspect capture groups, replacements, and highlighted matches side by side.
- Test edge cases before copying the final expression into your codebase.
Safe use tips
- Use redacted sample text when working with logs, emails, or user content.
- Try long inputs to catch patterns that may become slow or overly broad.
- Document what each capture group means before handing the expression to another developer.
Frequently Asked Questions
Which regex engine does this tester use?
It uses the JavaScript regular expression engine available in your browser.
Can I test regex replacements?
Yes. Switch to replacement mode, enter replacement text such as $1 or amp;, and preview the result instantly.
Are named capture groups supported?
Yes, when supported by your browser, named capture groups are shown in the match details.
Is my test text uploaded?
No. Regex matching runs in the browser, so your text stays local.