Regex Tester
Test and debug regular expressions in real-time. Match, replace, and validate patterns with preset templates.
What are Regular Expressions?
Regular expressions (regex) are patterns used to match character combinations in strings. They provide a powerful and concise syntax for searching, validating, and transforming text. Regex is supported by virtually every programming language, text editor, and command-line tool.
Enter your regex pattern and test string to see matches highlighted in real-time. Toggle flags like global (g), case-insensitive (i), and multiline (m) with a click. Switch to Replace mode to test substitution patterns using capture groups ($1, $2). Preset templates are available for common patterns like emails and URLs.
Developers use regular expressions for form input validation, log file parsing, data extraction from unstructured text, search-and-replace operations in code editors, and route matching in web frameworks. Regex is indispensable for tasks like cleaning CSV data, scraping web content, and enforcing string format rules.
Key regex concepts include character classes ([a-z], \d, \w), quantifiers (*, +, ?, {n,m}), anchors (^, $), and capture groups (parentheses). Lookahead (?=) and lookbehind (?<=) assertions enable advanced matching without consuming characters. Understanding greedy vs. lazy quantifiers is essential for writing efficient patterns.