TEXT & DEVELOPER TOOLS
Regex Tester
Test JavaScript regular expressions with live highlighting, capture groups, a replacement preview and a plain-English explanation.
Quick answer: Enter a pattern and some text. Matches highlight instantly, and the details table lists every group with its position.
Use Regex Tester ↓Loading the tool…
How to use Regex Tester
- Enter pattern and textSet flags with the checkboxes and type or paste your sample text.
- Review the matchesHighlighted matches, a table with groups and line:column positions, and a plain-English explanation.
- Replace or copyPreview a replacement using $1 or $<name>, or copy matches as text, JSON or JavaScript code.
Good to know
Common uses: Validating input, extracting data, writing search-and-replace rules and learning regular expressions.
Practical example: Pick “Email address” from the pattern library and paste a list of text to see every address highlighted.
Important limitation: The tester uses your browser’s JavaScript regex engine, so syntax follows JavaScript rather than PCRE or Python. Very slow patterns are stopped after about two seconds with a warning about catastrophic backtracking.
For sensitive work, read the privacy information and follow your organization’s data-handling policy.
How it works
Matching runs in a background worker so a bad pattern cannot freeze the page. Results are mapped back to your text for highlighting and positions.
Real-world uses
- Validating emails, dates and IDs
- Extracting data from logs
- Testing a replacement before running it in code
Tips for better results
- Start from the pattern library for common formats such as Indian PAN, GSTIN and PIN codes.
- Use named groups for readable replacements.
- Test edge cases and empty input.
Frequently asked questions
Which regex flavor is used?
JavaScript. Some PCRE or Python features, such as possessive quantifiers, are not available.
What if my pattern hangs?
It is stopped after about two seconds and you are told it may be catastrophic backtracking.
Can I test replacements?
Yes, with $1, $2 and $<name> references.
Does it explain patterns?
Yes. A plain-English breakdown appears under the pattern.
Is my text uploaded?
No. Testing happens in your browser.
Is the Regex Tester free?
Yes.