Regex Tester

What is Regex?

Regular Expression (Regex) is a formal language for expressing patterns in strings. It's used to search, extract, and replace strings that match specific patterns. Widely used in programming, data processing, text editing, and more.

What are Flags?

Flags modify how the regex engine behaves:

• g (global): Find all matches (not just the first one)
• i (ignore case): Case-insensitive matching
• m (multiline): ^ and $ match start/end of each line
• s (dotAll): . matches newline characters too
• u (unicode): Full Unicode support

What are Group Captures?

Parts enclosed in parentheses () are called groups, and matched portions can be captured separately. Example: (\d{3})-(\d{4}) captures two groups. These groups can be referenced as $1, $2, etc. when replacing.

How do I use the Replace feature?

Enter a value in the "Replacement" field to preview the result of replacing matched parts with another string. You can reference captured groups using $1, $2, etc. Example: Pattern (\w+)@(\w+), Replace $2@$1

Common regex patterns?

Examples of common patterns:

• Email: [a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}
• Phone (US): \d{3}-\d{3}-\d{4}
• URL: https?://[^\s]+
• Date (YYYY-MM-DD): \d{4}-\d{2}-\d{2}
• Numbers only: \d+

Precautions when testing regex?

Regex is powerful but can be complex. Keep these in mind:

• Overly complex patterns can cause performance issues
• Special characters (., *, +, ?, etc.) need to be escaped with backslash (\)
• Test thoroughly with various cases before using in production

Is my data safe?

Yes! All testing happens only in your browser. Your pattern and test strings are never sent to any server and are not stored anywhere.