Common use cases
- Form validation
- Check patterns for emails, IDs, slugs or user input.
- Text extraction
- Extract repeated patterns from logs or copied text.
- Replacement testing
- Preview cleanup rules before using them in code.
Development · free tool
Regex tester for JavaScript patterns, matches and replacements
Test JavaScript regular expressions, flags, matches and replacements.
Your tool
Regex Tester
Use it well
How to use Regex Tester
Steps
- Enter a regex pattern.
- Set JavaScript flags such as g or i.
- Paste sample text.
- Review matches and replacement output.
Limits and good practices
Good practices
- Use realistic test values when validating forms, exports or API payloads.
- Keep real customer, banking and production secrets out of public tools.
- Check the output format before copying it into a production workflow.
- Document whether a value is generated, validated, converted or only estimated.
Common mistakes
- Confusing valid format with real-world validity
- A generated or locally validated value can match a format without proving that it exists in an official system.
- Using real production data
- Public utilities are best for test data, demos, fixtures, QA and quick checks, not for confidential values.
FAQ
Frequently asked questions
Which regex flavor is used?
The tester uses JavaScript regular expressions, so behavior follows the browser RegExp engine.
Why can a regex be slow?
Some nested quantifiers can cause expensive backtracking. Simplify risky patterns before using them on large text.
Can I test replacements?
Yes. Enter replacement text to preview the transformed output.
Are my inputs sent to a server?
OnSubmit tools run in the browser whenever the task can be processed locally. Avoid pasting production secrets, real banking details or personal data into public tools.