Monoliths can block iteration speed. App Router modular design helps isolate concerns and keep delivery stable.
Why modular
When a single codebase grows past a few feature teams, changes collide and deployment risk rises. Co-locating each feature's UI, data, and server logic inside its own route segment keeps ownership clear.
Patterns that hold up
- Route-grouped features — group by domain, not by file type.
- Server components by default — push interactivity to small client islands.
- Typed data contracts — share Zod schemas across server and client.