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
Common 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?
The pattern runs in a separate browser worker that is stopped after 1.5 s, with pattern and text length limits.
What regex flavor is used?
JavaScript regular expressions, run in your browser (a runaway pattern is stopped after 1.5 s). Python spellings such as (?P<name>…), (?P=name), (?i), \A and \Z are accepted too.
What is a capture group?
A part of the pattern in parentheses whose matched text is returned separately.