Regex Tester — Multi-Language (JS / Python / Go / Ruby)

This tool supports JavaScript (RegExp), Python (re module), Go (regexp/RE2), and Ruby (Oniguruma). Each language has its own flag set and syntax conventions. The tool uses the browser's JavaScript engine for matching, but generates code snippets in the selected language and adapts named group syntax (?P<name> for Python/Go → (?<name> for JS).

Named groups let you reference captures by name instead of number. JavaScript uses (?<name>...) and $<name> in replacements. Python uses (?P<name>...) and \g<name>. Go uses (?P<name>...) and re.SubexpNames(). Ruby uses (?<name>...) and m[:name]. This tool normalizes all formats and shows named group values in the output.

No. Go uses the RE2 engine which deliberately excludes lookahead (?=...), negative lookahead (?!...), lookbehind (?<=...), and negative lookbehind (?<!...) because they can't be matched in linear time. If your pattern uses these features, it won't work in Go. The Lookahead preset will show matches in JS/Python/Ruby but is incompatible with Go.

By default, the dot (.) in a regex matches any character except newline (\n). With the s flag (called DOTALL in Python or (?s) in Go), dot also matches newline characters. This is essential for patterns that span multiple lines. JavaScript added the s flag in ES2018.

Replace mode runs your pattern against all test lines and applies the replacement string. Use $1, $2 for numbered groups and $<name> (JS/Ruby) or \g<name> (Python) for named groups. The output shows the full replaced string. This is equivalent to String.prototype.replace() in JS, re.sub() in Python, gsub() in Ruby, or regexp.ReplaceAllString() in Go.

The x flag allows whitespace and comments inside the pattern, making complex regex readable. Whitespace is ignored (use \s or [ ] for literal spaces), and # starts a comment to end of line. This is only available in Python and Ruby — JavaScript does not support it natively.