Renderer

In React, a renderer is the layer that connects the platform-independent core to a real output. The react package only knows about components, hooks and state; it does not know what a view is. A renderer supplies that knowledge. react-dom renders to the browser DOM, and React Native’s renderer renders to native views.

All renderers share the same engine, the reconciler, which does reconciliation, scheduling and hooks. Each renderer plugs in a host config: a set of functions that tell the reconciler how to create an instance, append a child, update props and commit changes on its platform. That design is why React’s model shows up in unexpected places — Ink renders to the terminal, React Three Fiber to a WebGL scene, and React Native Skia uses its own reconciler to draw to a canvas.

React Native’s renderer is the JavaScript half of the Fabric renderer. Its host config does not create views directly; it builds shadow nodes in C++ through JSI, and Fabric takes over from there. Host components such as View, Text and Image are the elements it understands; your own components are resolved down to those.

Why this matters day to day:

• react and react-native versions are locked together. The renderer is built from the React repository and shipped inside the react-native package, so it expects one exact React version. Upgrading react on its own produces an "Incompatible React versions" error at start-up. Upgrade both together, as the release notes specify.
• Not everything from React DOM applies. APIs that belong to react-dom, such as portals created with createPortal or DOM form actions, do not exist in React Native.
• One codebase, several renderers. React Native Web maps React Native’s components onto react-dom, which is how an app can target the browser without a new renderer.

When you read "React is platform-agnostic", the renderer is the reason that is true.