How it works
The tool builds a RegExp from your pattern and flags and runs it against your text, listing each match with its position and capture groups (including named groups). The replace preview uses String.prototype.replace, so $1, $& and $<name> work as in JavaScript.
Matching runs synchronously on the page. To limit the risk of a runaway pattern, input is capped at 20,000 characters, patterns at 500 characters and results at 1,000 matches, and patterns with nested quantifiers ask for confirmation first. These are safeguards, not guarantees.
Common uses
- Building and debugging validation patterns for forms.
- Extracting parts of log lines or text with capture groups.
- Previewing a find-and-replace before running it on real data.
- Learning how regex flags and groups behave.