Regex Tester
Test regular expressions with real-time highlighting.
What are regular expressions?
Regular expressions (regex) are search patterns used to find, validate, and manipulate text. They are fundamental in programming, system administration, data analysis, and text processing. Languages like JavaScript, Python, Java, and PHP support them natively.
A regex can be as simple as searching for a word or as complex as validating an email format. Special characters like . (any character), * (zero or more), + (one or more), [] (character set), and () (groups) allow building very specific patterns.
Frequently asked questions
What do the flags g, i, m, s mean?
g = search for all matches (not just the first), i = ignore case, m = ^ and $ apply per line, s = the dot (.) also matches line breaks.
How do I validate an email with regex?
{"A basic pattern is: [a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,}. However, perfect email validation with regex is extremely complex."}
Is it safe to process regex in the browser?
Yes, everything is processed locally. However, very complex patterns with many nested quantifiers can cause slowness (catastrophic backtracking).
Want to learn more? Read our complete guide →