Uses the browser’s JavaScript regex engine

The pattern is passed to the standard `RegExp` constructor with the selected `g`, `i`, `m`, `s`, and `u` flags. Results therefore describe JavaScript behavior, not PCRE, Python, .NET, Java, RE2, or another regex dialect. Delimiter slashes should not be entered in the pattern field.

Matches include structural detail

Each result reports its zero-based character index, complete matched text, numbered capture groups, and named groups. Global mode continues through the input and safely advances after a zero-length match. Output is capped at 1,000 matches so a broad expression cannot create an unlimited report.

Replacement follows JavaScript syntax

Enable replacement preview to test tokens such as `$&` for the complete match, `$1` for a numbered group, and `$<name>` for a named group. Global replacement requires the `g` flag. The preview is capped at one million characters even though the input limit is much smaller.

Execution is isolated and timed

Regular expressions can exhibit catastrophic backtracking. Matching and replacement run in a disposable Web Worker, not on the main interface thread. The worker is terminated if it does not finish within 750 milliseconds. This limit reduces page freezes but does not prove that a pattern is safe for production workloads.

Do not paste secrets or untrusted sensitive data into debugging tools. Processing is local, but browser extensions, shared devices, screenshots, clipboard history, and downstream copies can still expose content. Test performance with representative production limits and an engine matching the real application.