Regex Tester
Test regular expressions with live match highlighting and capture group display. Supports all JavaScript regex flags.
How to Use the Regex Tester
- Enter your regex pattern in the pattern input field (without the surrounding slashes).
- Select flags using the checkboxes: g (global), i (case-insensitive), m (multiline), s (dotAll), u (unicode).
- Type or paste test text into the test string area. Matches are highlighted in real time.
- View the match details below, including match positions and capture groups.
- Use the common patterns buttons to quickly insert popular regex patterns.
About Regular Expressions
Regular expressions (regex or regexp) are powerful patterns used to match character combinations in strings. They are a fundamental tool in programming, used for input validation, search and replace, text parsing, and data extraction. Every major programming language supports regex, though syntax details may vary slightly between implementations.
This tool uses JavaScript's built-in RegExp engine, which supports the ECMAScript standard. Common regex constructs include character classes ([a-z]), quantifiers (+, *, ?), anchors (^ and $), groups and capturing (parentheses), lookahead and lookbehind, and alternation (|). Mastering regex is an essential skill for developers, data engineers, and system administrators working with text processing tasks.
Frequently Asked Questions
A regular expression (regex) is a sequence of characters that defines a search pattern. It is used to match, find, and manipulate text. Regex is supported in virtually every programming language and is essential for input validation, text parsing, and search-and-replace operations.
Regex flags modify how the pattern matching works. Common flags include: g (global, find all matches), i (case-insensitive matching), m (multiline, ^ and $ match line boundaries), s (dotAll, dot matches newlines), and u (unicode, enables full Unicode support).
Capture groups are portions of a regex pattern enclosed in parentheses (). They allow you to extract specific parts of a match. For example, the pattern (\d{3})-(\d{4}) matching "555-1234" would capture "555" as group 1 and "1234" as group 2.