Regex Validator โ Syntax Check ยท Error Position ยท Unit Tests
Real-time ยท 26 features ยท AI explain ยท Unit tests ยท Diff mode ยท JS/Python/PHP ยท 100% browser
Validate regex syntax instantly with error position highlighting. Write PASS/FAIL unit test cases that run automatically as you edit โ the fastest way to verify your regex handles all edge cases correctly.
What is a Regular Expression?
A regular expression (regex) is a sequence of characters that defines a search pattern. Used for validation, parsing, text manipulation, and data extraction in virtually every programming language โ JavaScript, Python, PHP, Java, and more.
How to Use This Regex Tester
Type your regex pattern in the input field. Matches highlight in real-time in the test text panel. Use the flags (g/i/m/s/u/y) to modify matching behavior. Switch between Test, Replace, Unit Test, Diff, and Multi-string modes using the tabs above.
Frequently Asked Questions
How does regex validation work?
The validator compiles your pattern with the selected flags using the browser's native RegExp constructor. If the pattern is invalid, it shows the exact error message and highlights the input in red.
How do I write unit tests for a regex?
Switch to Unit Test tab. Add test strings with "Should MATCH" or "Should NOT match" expectation. Tests run automatically on every pattern change โ green โ means the test passes, red โ means the regex behaves unexpectedly.
What are the most common regex validation use cases?
Email validation, phone number validation (country-specific), URL validation, date format checking, password strength rules, username format enforcement, and form field validation are the most common uses.