Sift lets you build and test JavaScript regular expressions against your own text. As you type, matches are highlighted, capture groups (numbered and named) are listed, and you can preview a find-and-replace. Toggle the flags, try a preset, and copy the result. Everything runs in your browser; nothing is uploaded.

/ / g

Presets:

Test string

Matches highlighted

Matches & groups

Replace

Patterns use JavaScript's regular-expression engine — the same one that runs in browsers and Node. The g flag finds every match; without it, only the first is highlighted. In Replace, $1 to $9 insert numbered groups, $<name> a named group, and $& the whole match. Everything runs on your device.