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Regex Tester
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A full-featured browser-based regex tester. Enter a pattern, toggle flags (global, case-insensitive, multiline, dotAll, unicode), and see matches highlighted instantly in your test string. Switch to Replace mode to preview substitutions with group references ($1, $2). The match details panel shows every match with its start index, length, and all capture groups. Copy individual matches or the replaced output with one click. All processing runs locally - no data leaves your browser.
How to Use
- 1Enter your regex pattern in the pattern field between the / / delimiters
- 2Toggle flags below the pattern field: g for global, i for case-insensitive, m for multiline, s for dotAll, u for unicode
- 3Paste or type your test string in the Test String textarea - matches are highlighted instantly
- 4Switch to Replace mode and enter a replacement string to preview substitutions
- 5View the Match Details panel to see each match's index, captured groups, and copy individual values
Features
- Live match highlighting in the test string as you type
- 5 flag toggles: g (global), i (case-insensitive), m (multiline), s (dotAll), u (unicode)
- Match Details panel showing index, length, and all capture groups for each match
- Replace mode with group reference support ($1, $2, $&)
- Handles up to 500 matches with smart cycle-breaking for zero-length matches
- Copy all matches or individual match values with one click
- Clear invalid-pattern error display with human-readable message
- 100% browser-based - no data leaves your device
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