Test regular expressions safely
Write a pattern with flags and paste sample text. Matches, capture groups and positions update live; the replace tab shows the substituted result before you copy it.
Replaced result
How to use it
- Enter the pattern and flags (g, i, m, s, u …).
- Paste the sample text and watch the matches update live.
- Switch to Replace to preview the substitution, then copy the result.
Limits & formats
JavaScript (ECMAScript) regex flavor — lookbehind and named groups follow what your browser supports. Patterns run inside a Web Worker with a 1-second watchdog: a catastrophic-backtracking pattern is terminated and reported instead of freezing the page. Limits: 2,000-character pattern, 200,000-character sample, first 1,000 matches listed. This tool does not use AI and does not generate patterns for you.
Privacy
Everything is computed locally in this browser tab; nothing is sent or stored.
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