Regex Tester

g finds all matches instead of just the first, i ignores case, m makes ^ and $ match at line breaks, s lets the dot match newlines, u enables full unicode mode, and y (sticky) only matches starting exactly at the last index.

The tool builds your pattern with new RegExp inside a try/catch. If the syntax is invalid, for example an unclosed group like "(", it shows the browser error message instead of crashing. Fix the pattern and the results update instantly.

Parentheses in a pattern capture part of each match. The tool lists every group per match, numbered from 1, plus any named groups written as (?<name>...). Groups that did not participate in the match are shown as no match.

It runs testString.replace(regex, replacement) live. You can use standard replacement tokens: $1, $2 for capture groups, $& for the whole match, $<name> for named groups, and $$ for a literal dollar sign.

No. This regex tester is completely free with no login, and your pattern and test string are evaluated entirely in your browser. Nothing is uploaded to a server.