name: Next.js Architecture (FSD) description: Scalable project structure using Feature-Sliced Design (FSD). metadata: labels: [nextjs, architecture, fsd, folder-structure] triggers: files: ['src/features/', 'src/entities/', 'src/widgets/**'] keywords: [FSD, Feature Sliced Design, slices, segments]

Architecture (Feature-Sliced Design)

Priority: P2 (MEDIUM)

Adopt Feature-Sliced Design (FSD) for scalable applications. Warning: FSD introduces boilerplate. Use it only if the project is expected to grow significantly (e.g., 20+ features). For smaller projects, a simple module-based structure is preferred.

Strategy

1. App Layer is Thin: The app/ directory (App Router) is only for Routing.
   • Rule: page.tsx should only import Widgets/Features. No business logic (useEffect, fetch) directly in pages.
2. Slices over Types: Group code by Business Domain (User, Product, Cart), not by File Type (Components, Hooks, Utils).
   • Bad: src/components/LoginForm.tsx, src/hooks/useLogin.ts
   • Good: src/features/auth/login/ containing both.
3. Layer Hierarchy: Code can only import from layers below it.
   • App -> Widgets -> Features -> Entities -> Shared.
4. Avoid Excessive Entities: Do not preemptively create Entities.
   • Rule: Start logic in Features or Pages. Move to Entities only when data/logic is strictly reused across multiple differing features.
   • Rule: Simple CRUD belongs in shared/api, not entities.
5. Standard Segments: Use standard segment names within slices.
   • ui (Components), model (State/actions), api (Data fetching), lib (Helpers), config (Constants).
   • Avoid: components, hooks, services as segment names.

Structure Reference

For the specific directory layout and layer definitions, see the reference documentation.

• FSD Folder Structure

Integration with Next.js Core

• Server Actions: Place them in the model/ folder of a Feature (e.g., features/auth/model/actions.ts).
• Data Access (DAL): Place logic in the model/ folder of an Entity (e.g., entities/user/model/dal.ts).
• UI Components: Base UI (shadcn) belongs in shared/ui. Feature-specific UI belongs in features/*/ui.