Regex Tester
Test regular expressions against sample text.
Regular expressions extract, validate, and transform text patterns, but they are easy to get wrong. Utilitoo's Regex Tester lets you write a pattern, paste sample text, and see matches highlighted in real time so you can refine your expression before shipping it to production code.
Use it when validating email formats, parsing log lines, building search-and-replace rules, or debugging grep commands. QA engineers test edge cases, and backend developers verify input validation rules against tricky unicode and whitespace samples from real user submissions.
Iterate quickly: adjust flags, tweak capture groups, and watch matches update live. When your pattern works, copy it into your application. Pair with Diff Checker to compare pattern versions or JSON Validator when extracting structured data from API responses.
Testing runs entirely in your browser on Utilitoo. Your sample text and patterns are never uploaded. Free, private, and built for developers, data engineers, and power users who work with text patterns daily. Technical writers documenting validation rules and support agents testing customer input patterns both benefit from a sandbox that shows matches without deploying code changes. Saving a working pattern from Utilitoo directly into your codebase reduces trial-and-error cycles that slow down form validation and log parsing tasks.
Use Regex Tester when you need a private, fast pass on regex tester data. Test regular expressions against sample text. Validate surprising output on a staging sample before it influences production changes.
Common use cases
- Debugging a failing API or config by running Regex Tester on a staging sample before changing production.
- Preparing regex tester output to paste into a pull request, incident ticket, or team chat.
- Checking third-party regex tester payloads before wiring them into application code.
- Teaching regex tester concepts in a workshop without installing CLI tooling on every laptop.
- Comparing Regex Tester output with a teammate during pair review when formats disagree.
Tips & common mistakes
Regex Tester runs in your browser on Utilitoo - paste staging payloads without a server upload. Start with a small sample to confirm format, then process the full input. If output looks wrong, check truncation, encoding, and mixed line endings from terminals or log viewers. Pin the tab during active debugging and chain Related Tools instead of returning to the homepage.
Common errors
- No matches - check flags, escaping, and whether the pattern assumes multiline input.
- Catastrophic backtracking - nested quantifiers can freeze the tab on large inputs; simplify or test a smaller sample.
No matches found.
How to use
- Enter regex pattern.
- Add test string.
- View matches.
Frequently Asked Questions
How do I test a regular expression online?▼
Enter your regex pattern and flags, paste sample text, and Utilitoo highlights all matches instantly in your browser.
What regex flavor does this tool use?▼
Utilitoo uses JavaScript regular expressions, the same engine used in browsers and Node.js, so patterns transfer directly to your code.
Why is my regex not matching anything?▼
Check for missing flags like i for case-insensitive, unescaped special characters, or anchors ^ and $ that limit where matches can start.
Can I test regex for email validation?▼
Yes. Paste sample emails and refine your pattern until valid addresses match and invalid ones do not.
Is it safe to test regex against production log data?▼
On Utilitoo, yes. All matching runs locally. Your text and patterns are not sent to any server.
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Sort lines of text alphabetically.
Remove Duplicate Lines
Remove duplicate lines from text.
HTML Escape / Unescape
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