Regex Tester Guide — Master Regular Expressions
A comprehensive guide to regular expressions. Learn syntax, patterns, and test your regex with our free online regex tester tool.
What is a Regular Expression?
A regular expression (regex) is a sequence of characters that defines a search pattern. It is used for pattern matching in strings — validating input, extracting data, replacing text, and more. Every major programming language supports regex.
Common uses include: email validation, phone number formatting, log parsing, URL matching, and search-and-replace operations.
Basic Syntax
Literal characters: 'hello' matches the exact string 'hello'.
Metacharacters: . (any char), \d (digit), \w (word char), \s (whitespace), ^ (start), $ (end).
Quantifiers: * (0+), + (1+), ? (0 or 1), {n} (exactly n), {n,} (n+), {n,m} (n to m).
Groups and alternation: (abc) (capturing group), (?:abc) (non-capturing), a|b (a or b).
Character classes: [abc] (any of a,b,c), [^abc] (not a,b,c), [a-z] (range).