What Is a Regex Tester?
A regex tester lets you write and test regular expressions against sample text in real time. Regular expressions (regex) are powerful pattern-matching sequences used in text searching, validation, and data extraction across virtually all programming languages.
How to Use This Regex Tester
- Enter your regular expression pattern in the pattern field.
- Paste the test string in the input area.
- View highlighted matches and captured groups in the output.
- Adjust flags (global, case-insensitive, multiline) as needed.
Key Concepts
Regex uses special characters called metacharacters: . (any character), * (zero or more), + (one or more), ? (optional), ^ (start of string), $ (end of string). Character classes like [a-z] match ranges, and \d matches digits. Capturing groups use parentheses () to extract specific portions of matches. Lookaheads (?=) and lookbehinds (?<=) match positions without consuming characters.
Frequently Asked Questions
Which regex flavor does this tool use?
This tool uses JavaScript’s regex engine, which supports most common features including lookaheads, named groups, and Unicode escapes. Some features like lookbehinds require modern browsers.
How do I match email addresses with regex?
A basic email pattern is [a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}. However, fully RFC-compliant email validation is extremely complex. For production use, consider dedicated validation libraries.
What are non-greedy (lazy) quantifiers?
Adding ? after a quantifier (like *?, +?) makes it match as few characters as possible instead of as many. For example, <.*> greedily matches everything between the first < and last >, while <.*?> stops at the first >.