About Regex Tester
Regular expressions (regex) are powerful patterns for matching, searching, and manipulating text. This tester lets you write a regex pattern, apply it against test strings, and see all matches highlighted in real time. View capture groups, match indices, and total match count. Supports standard flags like global (g), case-insensitive (i), and multiline (m).
How to Use
- Enter your regex pattern in the pattern field.
- Set the desired flags (g, i, m, etc.).
- Enter the test string to match against.
- Click "Test" to see all matches highlighted.
- Review match details including capture groups.
Key Features
- ✓ Live match highlighting
- ✓ Support for all standard flags
- ✓ Display capture groups and indices
- ✓ Show total match count
Common Use Cases
- • Building and testing regex patterns for validation
- • Debugging regex in application code
- • Extracting patterns from log files
- • Learning regular expression syntax
Frequently Asked Questions
What is a regular expression?
A regular expression (regex) is a sequence of characters defining a search pattern. It is used for string matching, search-and-replace, and input validation across virtually all programming languages.
What do the flags mean?
Common flags: g (global — find all matches), i (case-insensitive), m (multiline — ^ and $ match line boundaries), s (dotall — dot matches newlines).
Why does my regex match differently than expected?
Common issues include greedy vs. lazy quantifiers, unescaped special characters, and incorrect flag settings. Test incrementally to isolate the problem.
Which regex flavor does this use?
This tool uses PHP PCRE (Perl-Compatible Regular Expressions), which is compatible with most programming languages.