What is the Regex Tester?
The Regex Tester is a free online tool for testing regular expressions against sample text with real-time match highlighting. This regex tester online shows you exactly what your pattern matches, displays all capture groups, and helps you validate regex patterns before using them in your code. All processing happens in your browser — no text data leaves your device.
How to Use the Regex Tester
- Enter your regular expression pattern in the top input field
- Add your test text in the main text area below
- Select flags as needed: global (g), case-insensitive (i), multiline (m), or dotall (s)
- Watch matches highlight in real-time as you type
- View the match count and all capture groups in the results panel
- Copy matched text or groups directly to your clipboard
When to Use This Tool
This regex tester online is essential when you need to:
- Validate patterns before deployment — test regex in form validation, API filters, database queries, or cron expression fields before pushing to production
- Debug complex expressions — see exactly which parts of your pattern match and identify issues with capture groups or lookarounds
- Learn regex syntax — experiment with different patterns and flags, or reference the Regex Cheat Sheet for common patterns
- Extract data — test patterns for parsing log files, extracting URLs, or cleaning up text data
Frequently Asked Questions
What regex flavours does this tester support?
This tool uses JavaScript’s native regex engine, which supports most common regex features including lookaheads, lookbehinds, named capture groups, and Unicode property escapes. The syntax is compatible with ECMAScript 2018+ and works in all modern browsers.
Can I save my regex patterns?
Your most recent pattern and test text persist in your browser’s local storage, so they’ll be there when you return. For long-term storage, bookmark the page or copy your pattern to a note-taking app.
Can I use this tool as a regex generator?
The Regex Tester is built for validating and debugging patterns rather than generating them from plain English. To use it as part of a regex generator workflow, write or generate your pattern using an AI tool or the Regex Cheat Sheet, then paste it here to verify it matches exactly the text you expect. Real-time highlighting makes it easy to catch edge cases before the pattern reaches your code.
What is regular expression testing and why does it matter?
Regular expression testing means running a regex pattern against real sample text to confirm it matches only the intended strings — not too much, not too little. Skipping this step is a common source of production bugs: a pattern that looks correct can silently fail on edge cases like empty strings, Unicode characters, or unexpected whitespace. This tool shows every match in real time so you can stress-test patterns before they reach your application.
Does this tool work for testing regex in Python, Java, or other languages?
This tool runs JavaScript’s regex engine (ECMAScript 2018+), which shares most syntax with other languages but has a few differences. Python’s re module and PCRE (used by PHP, Ruby, and Perl) support named groups with (?P<name>...) syntax, while JavaScript uses (?<name>...). Java uses \\ in string literals where other languages use \. Use this tool for rapid pattern iteration, then verify in your target language’s runtime before deploying.
Test your regular expressions now with our free regex tester online — also useful for validating URL patterns. No sign-up required.