Regex Tester: Debug Regular Expressions in Your Browser
Test JavaScript regular expressions with live match highlighting, capture group inspection, replace preview, and a library of common patterns. Debug regex before pasting into code, validators, or search-and-replace workflows.
Key Features
- Real-time match highlighting with first-match emphasis
- Flags: global, ignore case, multiline, dotAll, unicode
- Matches list with index ranges and one-click copy
- Capture groups table with named group support
- Replace preview with $1, $2 backreferences
Common Use Cases
- Validate email, URL, and date patterns before production
- Debug failing regex from log parsers or form validators
- Test replace rules for bulk text transformation
- Learn regex syntax with instant visual feedback
- Compare match counts across pattern variations
Benefits
- Uses the same RegExp engine as your browser JavaScript
- 100ms debounce keeps typing smooth on large test strings
- Common pattern library loads proven regex in one click
- Completely private — patterns may contain sensitive data
Why test regex online?
Regular expressions are powerful but easy to get wrong. A live tester lets you see matches, capture groups, and replacement output instantly — without writing a script or refreshing a page.
This tool runs entirely in your browser using JavaScript's RegExp engine. Your patterns and test strings never leave your device.
Flags and replace mode
Toggle g (global), i (case-insensitive), m (multiline), s (dotall), and u (unicode) flags to match how your regex runs in production code.
Use the Replace tab with $1, $2, and named backreferences to preview substitutions before pasting them into your application.
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