Free Online Regex Tester

A regular expression (regex or regexp) is a sequence of characters that defines a search pattern for pattern matching within strings -- finding, extracting, validating, or replacing text that matches a specific format. They are supported in most programming languages including JavaScript, Python, Java, PHP, and many text editors.

Enter your regular expression pattern in the input field, choose the appropriate regex flags, and paste or type your test string. The tool will instantly highlight all matches and show detailed information about each match including its position and any captured groups.

Yes, all pattern matching and text processing happen locally in your browser. Your regular expressions and test data never leave your device. No information is uploaded to any server, logged, or stored.

i (ignore case) makes matching case-insensitive. g (global) finds all matches in the string instead of stopping after the first match. m (multiline) treats ^ and $ as matching the start and end of each line. u (unicode) enables full Unicode support, allowing patterns to match characters beyond the Basic Multilingual Plane (like emojis).

Use the global flag (g) when you need to find all occurrences of a pattern in a string, not just the first one -- for example, when extracting all email addresses from a document, all hashtags from a social media post, or all numbers from a log file.

Capture groups use parentheses () to extract specific parts of a match during pattern matching. Group 0 is always the full match, group 1 is the first parenthesized sub-expression, group 2 the second, and so on. In replacements, reference groups with $1, $2, etc.

Special characters that carry syntactic meaning must be escaped with a backslash to match them literally. These metacharacters include: . * + ? ^ $ ( ) [ ] { } | \. For example, to match a literal period use \., and to match a backslash itself use \\\\