Regex Tester Online for Developers
Use this free Regex Tester Online to test regular expressions against sample text in your browser. The tool provides live match highlighting, JavaScript-compatible flags, capture group details, replacement previews and clear invalid-pattern messages. It is useful for developers, QA testers, students and anyone working with text patterns.
People in the USA, UK, India and other regions can use the browser-based regex testing workflow for common tasks such as checking email patterns, URLs, phone numbers, dates, identifiers, whitespace, repeated values and custom validation rules.
How to Test a Regular Expression
- Enter a JavaScript-compatible regular expression in the pattern field.
- Choose the g, i and m flags when needed.
- Enter or paste sample text into the test string field.
- Review the match count, highlighted matches and capture groups.
- Optionally enter replacement text to preview how matched content can be replaced.
Regex Flags: g, i and m
The g flag searches for multiple matches, i makes matching case-insensitive, and m changes how the ^ and $ anchors work across multiple lines. The tester uses the browser's JavaScript regular expression engine, so results follow JavaScript RegExp behavior.
Common Regex Testing Examples
You can test patterns for email addresses, URLs, phone numbers, dates, numbers, usernames, whitespace, words and custom application validation. For example, an email pattern such as [A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,} can be tested against several sample addresses to see which strings match.
Capture Groups and Replacement
Parentheses create capture groups that can help you extract parts of a match. When replacement text is entered, the tester previews the replacement result using JavaScript replacement syntax such as $1 for the first captured group.
Invalid Regex Error Handling
If a pattern contains invalid JavaScript regular expression syntax, the tester catches the error and displays a readable message. This helps you correct missing brackets, invalid escapes, unsupported flags or other syntax issues without breaking the page.
Browser-Based Regex Testing
The core matching workflow runs locally in the browser. Avoid entering passwords, private keys, API tokens or other confidential information into any online tool unless you have reviewed the security requirements for your use case.