Debug regular expressions against sample text. Inspect matches, capture groups and replacement output. This tool uses JavaScript regular expression syntax; PHP and Python engines may behave differently.
Test regular expressions online
Use this regex tester to check patterns against sample text while developing validation rules, parsers, search features and text transformations. The tool highlights matches, lists capture groups and previews replacement output using the JavaScript regular expression engine.
How to use the regex debugger
- Enter a regular expression without surrounding slash delimiters.
- Select supported flags such as global, case-insensitive or multiline.
- Paste sample text into the test area.
- Review matches, capture groups and replacement preview.
Regex compatibility
This tool uses the browser JavaScript RegExp implementation. Regular expression syntax is not identical across JavaScript, PHP PCRE, Python and other engines. Test the final expression in the runtime used by your application before shipping it.
Frequently asked questions
Does this tester support lookaheads?
It supports lookaheads and other constructs supported by the browser JavaScript engine.
Why does my PHP regex behave differently?
PHP commonly uses PCRE, which has features and behavior that can differ from JavaScript regular expressions.
Related developer tools on SkillHost
Use these connected utilities as part of the same development workflow: check environment configuration files, inspect application log output, validate structured JSON data. You can also browse all developer tools or explore practical developer projects and source-code examples on SkillHost.
Official documentation and further reading
For deeper implementation details, refer to the MDN regular expressions guide. Use the official specification or documentation to confirm runtime-specific behavior before deploying changes.
Privacy and browser processing
Core processing runs locally in your browser. SkillHost does not receive the text, code, tokens or data entered into this tool. Anonymous page-open and successful-use events may be recorded by SkillHost Tool Analytics; analytics events do not contain the submitted content.