What Is a Regular Expression?

A regular expression (regex) is a sequence of characters that defines a search pattern. Used in programming for matching, searching, and replacing text. For example: /^[a-z]+@[a-z]+\.com$/i matches simple email addresses.

Essential Regex Syntax

• . — matches any single character
• * — matches 0 or more of the previous
• + — matches 1 or more of the previous
• ? — matches 0 or 1 of the previous (optional)
• ^ — start of string
• $ — end of string
• [abc] — matches a, b, or c
• \d — digit (0-9)
• \w — word character (a-z, A-Z, 0-9, _)
• \s — whitespace

How to Use the Regex Tester

1. Open Regex Tester.
2. Enter your regex pattern in the pattern field.
3. Enter test text below.
4. Matches are highlighted in real time.
5. Adjust flags (g=global, i=case-insensitive, m=multiline) as needed.

Common Regex Patterns

• Email: /^[\w._%+-]+@[\w.-]+\.[a-z]{2,}$/i
• Phone: /^[+]?[(]?[0-9]{3}[)]?[-\s.]?[0-9]{3}[-\s.]?[0-9]{4}$/
• URL: /https?:\/\/(www\.)?[\w-]+\.\w+/