Formula: /pattern/flags → test string → matches[]
Regular expressions (regex) are patterns used to match character combinations in strings. They're essential for validation (emails, phone numbers), search-and-replace, and text parsing. This tool takes a regex pattern and a test string, then shows all matches with their positions. Common syntax: . (any char), * (zero or more), + (one or more), \d (digit), \w (word char), [abc] (character class), ^ (start), $ (end).