Question 1

What are regex flags?

Accepted Answer

Regex flags modify how the pattern is applied. Common flags are: g (global - find all matches), i (case-insensitive), m (multiline - ^ and $ match line boundaries), and s (dotAll - . matches newlines too).

Question 2

What is a capture group in regex?

Accepted Answer

A capture group is a part of a regex pattern wrapped in parentheses, e.g. (\d+). It captures the matched text so it can be referenced or extracted. Named groups use (?<name>...) syntax.

Question 3

How do I match across multiple lines in regex?

Accepted Answer

Enable the m (multiline) flag to make ^ and $ match the start and end of each line rather than the whole string. Enable the s (dotAll) flag to make . match newline characters as well.

Question 4

Is my regex or test text sent to a server?

Accepted Answer

No. All matching runs locally in your browser using the built-in JavaScript RegExp engine. Nothing is transmitted - your patterns and test strings stay on your device.

Regex Tester