Regular Expression (Regex) Tester
Test, debug, and visualize JavaScript regular expressions with real-time match highlighting, capture group inspection, and string substitution.
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Frequently Asked Questions
Does this regex tester run in my browser? ↓
Yes, 100%. The regular expression engine is your native browser JavaScript RegExp engine. Your test strings and data are never sent to any remote server.
What regex flags are supported? ↓
We support all standard ECMAScript flags: g (global search), i (case insensitive), m (multiline), s (dotAll / singleline), u (unicode), and y (sticky).
How does the replace/substitution preview work? ↓
You can test string replacements using standard JavaScript syntax, including backreferences like $1, $2 for numbered capture groups, $& for the entire match, and $<name> for named capture groups.
Can this tool cause my browser to freeze with catastrophic backtracking? ↓
We run regular expressions with execution guards. However, expressions with exponential catastrophic backtracking (such as nested quantifiers like (a+)+$) may temporarily block the UI thread. Use targeted quantifiers for optimal performance.