Question 1

What is a regular expression?

Accepted Answer

A regular expression (regex) is a sequence of characters that defines a search pattern. Used in programming and text processing to find, match, and manipulate strings. They are supported in nearly every programming language.

Question 2

What do regex flags do?

Accepted Answer

Flags modify how a regex pattern is applied: g (global) finds all matches instead of just the first; i (case-insensitive) matches regardless of letter case; m (multiline) makes ^ and $ match line boundaries; s (dotall) makes the dot . match newlines too.

Question 3

How do I match capture groups in regex?

Accepted Answer

Use parentheses to create capture groups: (\d+) captures one or more digits. This tool shows each capture group value in the match details. Named groups use (?<name>pattern) syntax.

Question 4

What regex engine does this use?

Accepted Answer

This tool uses the JavaScript built-in RegExp engine, which implements a subset of PCRE-style regex syntax. It supports lookahead, lookbehind (in modern browsers), named groups, and most standard regex features.

Regex Tester

Regular Expression Tester