Which regex flags does the tool support?

The tool supports standard JavaScript flags: g (global), i (case-insensitive), m (multiline), s (dotAll - makes . match line breaks) and u (unicode).

How do captured groups work in replace?

Groups are defined with parentheses in the regex. In the Replace field, use $1 for the first group, $2 for the second, and so on. For example: regex (\w+)@(\w+) with replace $2.$1 turns 'user@domain' into 'domain.user'.

Can I test regex on large files?

Yes. Use the 'Upload (.txt)' button to load text files and test your regex on the entire content. The tool processes everything locally in the browser.

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Regex Tester

Test regular expressions.

Runs in browser

Test and debug regular expressions in real time. Visualize matches, captured groups, indexes, and preview replacements. Supports flags (g, i, m, s, u) and presets for common cases.

Test text

Live highlight

Matches / Groups

Preview / Result

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