What is Regex Tester?
A regular expression (regex) is a powerful pattern used to search, match and manipulate text. A regex tester lets you write a pattern, apply flags, and instantly see which parts of a sample text it matches, with every match highlighted. This immediate feedback makes it far easier to build and debug complex patterns.
You can experiment with patterns for emails, phone numbers, dates and more, and the tool reports how many matches were found and flags any syntax errors.
How to Use the Regex Tester
- Enter your regular expression pattern.
- Add flags such as g, i or m if needed.
- Paste the text you want to test against.
- Watch matches highlight live and see the match count update.
Features of Our Regex Tester
- Live match highlighting as you type
- Support for common flags (g, i, m and more)
- Clear match count and error reporting
- Safely handles patterns that could loop
- Works with any sample text
- Runs entirely offline
Benefits & Use Cases
Developers build and refine patterns for validation, search-and-replace and data extraction. Seeing exactly what a pattern matches prevents subtle mistakes and speeds up learning regex.
Because everything runs locally, you can test patterns against sensitive sample data without any privacy concerns.
The Regex Tester is completely free, needs no sign-up or installation, and runs entirely in your browser — nothing you enter is uploaded to a server, so your data stays private. It works on desktop, tablet and mobile, in light or dark mode.
Tips & Best Practices
Build your pattern here and watch every match highlight live, with a running count — far faster than guessing in code. Add flags as needed: g to find all matches, i to ignore case, m for multiline anchoring. The engine is JavaScript's, so patterns behave exactly as they will in browser and Node.js code.
Once the pattern is right, drop it into the Find and Replace tool to transform real text, and confirm the before and after with the Text Diff Checker.
FAQ about Regex Tester
Which regex flavour does it use?
It uses JavaScript's regular expression engine, so patterns behave exactly as they would in browser and Node.js code.
What do the flags mean?
Common flags include g for global (find all matches), i for case-insensitive, and m for multiline anchoring. You can combine them.
Why is the global flag added automatically?
The tester needs to find every match to highlight them all, so it ensures the g flag is present even if you omit it.
Is my test data private?
Yes. All matching happens in your browser, so your patterns and text never leave your device.