What is Regex Tester?
Regex Tester is a free online tool to test regular expressions against sample text. See every match and capture group with i, m and s flags, protected by a ReDoS timeout guard.
Test regular expressions online safely. See matches and capture groups with length/timeout guards — free regex tester on Fah Swe Tools.
Key features
- Matches and capture groups
- Case-insensitive, multiline and dotall flags
- ReDoS timeout protection
- Free, no signup
Popular uses
- Build validation patterns for emails and phone numbers
- Debug search-and-replace expressions
- Learn regex step by step
Also known as: Regex Checker, Regular Expression Tester, Regex Online.
How it works
- Enter pattern and test string.
- Toggle i / m / s flags.
- Inspect matches and capture groups.
FAQ
ReDoS?
We enforce pattern/subject length limits and a short match timeout.
What regex flavor is used?
Python's re module, which is very close to PCRE/JavaScript for common patterns.
What is a capture group?
A part of the pattern in parentheses whose matched text is returned separately.