Regex Tester

How the matching works

This tool builds a native JavaScript RegExp from your pattern and flags, then scans the entire test string for every match rather than stopping at the first one, adding the g flag internally if you left it off so you always see the full picture. Each match is listed with its zero based starting index and any capture groups it produced, and every match is also highlighted directly in the test string so you can see exactly what got selected.

What the flags do

The g flag finds every match instead of only the first. The i flag makes matching case insensitive. The m flag changes ^ and $ to match the start and end of each line instead of only the whole string. The s flag lets the dot character match line breaks as well. You can combine flags, like gi for a case insensitive global search, by typing them together.

Reading capture groups

Parentheses in a pattern create a capture group, a piece of the match you can reference separately, and this tool lists each group's value under its match using the standard $1, $2 notation. A group that did not participate in a particular match, for example one side of an alternation like (cat|dog), shows as no match rather than an empty string, which is the correct distinction JavaScript itself makes.