Most tools sit on one side of a line. AI code-review tools read the diff but never run it, so they guess "this could be null." Black-box E2E tools drive a real browser but see only the DOM. Qlane boots your whole app in a sandbox and tests it from the inside - browser, shell, source, plus connectable logs and database - so it reports only bugs that actually reproduce, and traces each to its root cause. runs your app, not just your code.