The Developer's Guide to Regular Expressions

What is Regex?

A regular expression (regex) is a pattern that describes a set of strings. Regex engines are built into every major language (JavaScript, Python, C#, Java, PHP, Go).

Basic Syntax

• . — Any character except newline
• \d — Any digit (0–9)
• \w — Word character (letters, digits, underscore)
• \s — Whitespace
• ^ — Start of string
• $ — End of string

Quantifiers

• * — Zero or more    + — One or more
• ? — Zero or one    {3} — Exactly 3    {2,5} — Between 2 and 5

Real-World Examples

// Validate email
/^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$/

// Match ISO date
/\d{4}-\d{2}-\d{2}/

Try them all in our live Regex Tester.