Test Regex Patterns Step by Step

Navigate to OnlineTools4Free Regex Tester. The tool provides a pattern input, a test string area, and real-time match highlighting.

Start with a basic pattern like \d{3}-\d{4} (matches phone number fragments like 555-1234). Type the pattern in the regex field and paste test text below. Matches are highlighted instantly.

Toggle regex flags: g (global — find all matches, not just the first), i (case-insensitive), m (multiline — ^ and $ match line boundaries), s (dotAll — . matches newlines). Most use cases need the g flag.

Wrap parts of your pattern in parentheses to create capture groups. For example, (\d{3})-(\d{4}) captures the area code and number separately. The tool shows each group's captured text.

Add test strings that should NOT match alongside ones that should. Verify that your pattern rejects invalid input (too many digits, wrong format, unexpected characters). A regex that matches too broadly is as problematic as one that misses valid input.

Iterate on your pattern until it matches exactly what you need. Copy the final regex for use in your code. The tool provides the pattern in JavaScript, Python, and PHP syntax.