Developer Tools
Regex Tester
Test JavaScript regular expressions against sample text in real time. Toggle the g, i, m, s, u and y flags, see every match highlighted, and inspect capture groups and the total match count — all in your browser, no libraries.
Your input is processed locally in your browser. It is not uploaded to Dueneo.
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How to use
- 1
Enter your pattern
Type a regular expression without the surrounding slashes. The flags are managed separately via the toggle buttons.
- 2
Toggle flags
Click any of g, i, m, s, u, y to add or remove that flag. The pattern is re-run instantly every time you change a flag.
- 3
Type your sample text
Any text you paste into the test area is matched against the pattern in real time. Matches are highlighted in amber.
- 4
Inspect matches and groups
The matches table lists each match, its character index and capture groups. Use Copy matches to grab every matched string.
Common use cases
- Validate an email, phone or URL pattern before deploying it.
- Extract every match from a log file for further analysis.
- Debug a regex that unexpectedly fails or matches too much.
- Learn the effect of each regex flag (g, i, m, s, u, y) interactively.
Limitations
- Uses JavaScript's
RegExpengine — PCRE-only features like lookbehind on older engines may not be available. - Empty matches with the global flag can produce surprising indices; the tool guards against infinite loops but the table may show contiguous positions.
- Sample text larger than ~500 KB will feel sluggish because highlighting runs on every keystroke.