Nextjs App

When this skill is active, follow this 7-step discipline for Next.js App Router development:

1. Default to Server Components

Every component is a Server Component unless it needs interactivity:

• Server Components can async/await directly, access databases, read files, and call APIs without exposing secrets
• Add 'use client' only when the component uses hooks (useState, useEffect), event handlers, or browser APIs
• Push 'use client' boundaries as low as possible — wrap the interactive leaf, not the page

2. Route and Layout Design

Plan the route tree before creating files:

• app/<route>/page.tsx for pages, app/<route>/layout.tsx for shared UI
• Use route groups (marketing), (dashboard) to organize without affecting URLs
• Co-locate loading.tsx, error.tsx, and not-found.tsx at each route segment
• Use generateStaticParams for routes that can be statically generated at build time

3. Data Fetching Strategy

Choose the right data pattern for each component:

• Server Components: fetch() directly in the component — no client-side state management needed
• Dynamic data: use cache: 'no-store' or revalidate: 0 for data that changes per request
• Static data: default fetch() caching or revalidate: 3600 for content that changes infrequently
• Client-side: use SWR or TanStack Query only for data that must update without navigation (real-time, optimistic UI)

4. Server Actions for Mutations

Use Server Actions instead of API routes for form submissions and mutations:

• Define with 'use server' at the top of the function or file
• Accept FormData or typed arguments, return structured results
• Validate input with zod on the server — never trust client data
• Call revalidatePath() or revalidateTag() after mutations to update cached data

5. Caching Tiers

Understand and configure each caching layer:

• Request memoization: duplicate fetch() calls in the same render are deduplicated automatically
• Data cache: fetch() responses cached across requests — control with revalidate or cache options
• Full route cache: statically rendered routes are cached as HTML — use dynamic = 'force-dynamic' to opt out
• Router cache: client-side cache of visited routes — use router.refresh() to invalidate

6. Middleware and Edge

Use middleware for cross-cutting concerns:

• Authentication checks, redirects, and header manipulation in middleware.ts at the project root
• Keep middleware lightweight — it runs on every matching request
• Use matcher config to limit which routes trigger middleware
• Edge Runtime functions for latency-sensitive operations: geolocation, A/B testing, bot detection

7. Verify the Build

Confirm the application works in production mode:

• npx next build — zero errors, check for unexpected dynamic routes
• npx next lint — all lint rules pass
• Review the build output: static vs dynamic pages, bundle sizes, route segments
• Test Server Actions with form submissions — they must work without JavaScript activated
• If any step fails, fix the issue and re-run the entire chain

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