Regex Tester & Debugger

A regular expression (regex) is a sequence of characters that defines a search pattern. It is used for pattern matching in strings — finding, replacing, or validating text. Regex is supported in virtually all programming languages.

g (Global) finds all matches instead of just the first. i (Case Insensitive) ignores upper/lowercase differences. m (Multiline) makes ^ and $ match line starts/ends, not just string starts/ends. s (Dotall) makes . match newline characters too.

Capture groups are created with parentheses (). They extract specific parts of a match. Named groups use (?<name>...) syntax. For example, (?<year>\d{4})-(?<month>\d{2}) would capture year and month separately from a date string.

Common mistakes include: forgetting to escape special characters (., *, +, ?, [, ], etc.), not using the global flag when you want all matches, greedy vs. lazy matching confusion (use .*? instead of .* for lazy), and backtracking issues with nested quantifiers.

Yes. All regex testing happens entirely in your browser. No data is sent to any server. The tool uses JavaScript's native RegExp engine.