Regex Tester
Test regular expressions live with match highlighting and capture groups.
This regex tester online lets you write a regular expression, paste sample text and see matches highlighted as you type. It is useful when you are building a pattern to validate an email, pull numbers out of a log, clean up a CSV or rewrite text with capture groups, and you want fast feedback instead of running your whole program each time. Test the pattern against several sample strings, check which parts are captured by each group, and adjust flags such as global, case-insensitive or multiline. The tester runs on the JavaScript regular expression engine built into your browser, so results match what you would see in JavaScript. Other languages such as Python, Java, C#, .NET, PHP and PowerShell share most syntax but differ on some features like lookbehind or named groups, so check those details before copying a pattern across. Everything runs locally. Your patterns and test text are never uploaded, there is no account, and it keeps working offline.
Frequently asked
Which regex engine does this tester use?
It uses the JavaScript engine in your browser, so results match JavaScript behavior. Patterns for Python, Java, C#, .NET, PHP or PowerShell usually work for basic cases but may differ on advanced features.
Can I use it as a regex tester for Python or Java?
You can prototype simple patterns here, then confirm them in your target language. Features such as named group syntax, lookbehind and flags can differ between languages.
Is my test text uploaded anywhere?
No. Matching runs entirely in your browser, and nothing is sent to a server. You can test with private logs or data safely.
Is this regex tester free and does it need an account?
It is free with no sign-up. Once the page has loaded it also works offline.
More Format & Dev tools
- JSON FormatterFormat, validate, minify and explore JSON — handles huge inputs without freezing the tab.
- SQL FormatterFormat MySQL, PostgreSQL and T-SQL with configurable indentation.
- Markdown PreviewRender Markdown live with GFM support and copy as clean HTML.
- Base64 Encode / DecodeEncode and decode Base64 text and files in your browser.
- JWT DecoderInspect JWT header, payload and expiry — tokens never leave the page.
- Diff CheckerCompare two texts and see additions and removals line by line.
- Cron BuilderBuild cron expressions and read them back in plain English.