What is a regular expression?

A regular expression (regex) is a sequence of characters that defines a search pattern. It's used for pattern matching in strings, text processing, and validation. Regex is supported in most programming languages and text editors.

How do I test a regular expression?

Enter your regex pattern in the pattern field, add a test string to match against, select flags (global, case-insensitive, etc.), and the tool will show all matches in real-time. Matches are highlighted and grouped for easy inspection.

What are regex flags?

Flags modify how the regex pattern is matched: 'g' (global) finds all matches, 'i' (ignoreCase) makes matching case-insensitive, 'm' (multiline) makes ^ and $ match line boundaries, 's' (dotAll) makes . match newlines, 'u' (unicode) enables full Unicode support, and 'y' (sticky) matches only from the last index.

Can I build regex patterns visually?

Yes! Use the Builder tab to construct regex patterns step by step. You can test your pattern in real-time as you build it, making it easier to learn and debug regular expressions.

What if my regex pattern is invalid?

The tool will display an error message explaining what's wrong with your pattern. Common issues include unclosed brackets, invalid escape sequences, or incorrect quantifier usage. Fix the error and try again.

Are my patterns stored or saved?

No, all processing happens entirely in your browser. We never see, store, or transmit any of your regex patterns or test strings. Your privacy and data security are completely protected.

🔎 Regex Tools - Tester & Builder

Test and build regular expressions online for free. Real-time matching, flag options, group capture, visual builder, and syntax highlighting. Perfect for developers and programmers.