Free Online Regex Tester
Test regular expressions against real data instantly — live match highlighting, capture groups, and a find-and-replace preview. Nothing you type here leaves your browser.
How this tool works
Everything runs in a background thread inside your own browser — your pattern and test string are never sent anywhere. Matching runs in a Web Worker with a hard timeout, so a runaway pattern (catastrophic backtracking) can't freeze the page; you'll get a clear error instead of a hung tab.
Toggle g (global — find every match, and replace every occurrence instead of just the first), i (case-insensitive), m (multiline, so ^/$ match line boundaries), and s (dot matches newline too).
Is this regex tester free to use?
Yes, completely free with no login and no usage limit.
Does my pattern or test data get sent to a server?
No. Matching happens entirely client-side in your browser using a sandboxed Web Worker. Nothing you type is transmitted or stored.
What happens if my regex hangs (catastrophic backtracking)?
The match runs on a 1.5-second timeout in a separate thread. If it doesn't finish in time, the worker is terminated and you'll see a message asking you to simplify the pattern — the page itself never freezes.
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