Understanding the _rsc Query Parameter
The _rsc identifier is a specialized query parameter and file extension suffix used primarily within the Next.js framework to manage the delivery of React Server Components (RSC). In modern web architectures utilizing the App Router, _rsc requests are triggered during client-side navigation to fetch the serialized data required to render server-side logic without performing a full browser refresh.
Unlike traditional Server-Side Rendering which returns a complete HTML document, an _rsc request returns a stream of serialized data. This payload contains the instructions necessary for the React Flight Runtime to reconstruct the Virtual DOM tree on the client. According to the Next.js Documentation, this approach enables Partial Rendering, where only the changed segments of a layout are updated, significantly improving Web Performance.
The _rsc payload includes several key pieces of information: the rendered output of server components, placeholders for Client Components (known as client references), and any props passed from the server to the client. This allows for a seamless Hydration process where the client-side state is preserved even as new server-rendered content is integrated into the DOM. As noted in the React Labs update, this architecture helps reduce the JavaScript bundle size by keeping heavy dependencies on the server.