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Developer Tools
Regex Tester
Regular expressions are powerful for validation, search and text extraction — and easy to get wrong. This free regex tester lets you try patterns against sample input with live match highlighting.
Use standard JavaScript RegExp syntax and flags (g, i, m, s, u, y). Matches update as you type so you can iterate quickly while writing patterns for forms, logs or parsers.
All testing is client-side. Complex patterns on huge texts may be slow; keep samples reasonably sized.
Interactive tool
Without surrounding slashes
2 matches
Highlighted matches
Contact us at hello@example.com or support@freeuktools.com for help.
| # | Match | Index |
|---|---|---|
| 1 | hello@example.com | 14 |
| 2 | support@freeuktools.com | 35 |
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How to use this tool
- Enter your regular expression (without surrounding slashes).
- Select flags such as global (g) or case-insensitive (i).
- Paste the text to test against.
- Review match list and highlighted results.
Frequently asked questions
Which regex flavour is used?
JavaScript’s RegExp engine (ECMAScript), as implemented in your browser.
Do I need to include slashes?
No. Enter the pattern only; flags are chosen separately. Slashes are for regex literals in code, not required here.
Why is there a warning about catastrophic backtracking?
Some patterns can run extremely slowly on certain inputs. If the page freezes, simplify the pattern or shorten the test string.
Can I use lookbehind?
Yes if your browser supports it (modern Chromium, Firefox and Safari generally do).