nextjs-best-practices – Data & Science skill for AI agents

Next.js Best Practices

> Principles for Next.js App Router development.

---

1. Server vs Client Components

Decision Tree

Does it need...?
│
├── useState, useEffect, event handlers
│   └── Client Component ('use client')
│
├── Direct data fetching, no interactivity
│   └── Server Component (default)
│
└── Both? 
    └── Split: Server parent + Client child

By Default

| Type | Use |

|------|-----|

| Server | Data fetching, layout, static content |

| Client | Forms, buttons, interactive UI |

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2. Data Fetching Patterns

Fetch Strategy

| Pattern | Use |

|---------|-----|

| Default | Version/config dependent; current fetch defaults are uncached |

| Explicit cache | fetch(url, { cache: "force-cache" }) when data may be shared |

| Revalidate | ISR (time-based refresh) |

| No-store | Dynamic (every request) |

Data Flow

| Source | Pattern |

|--------|---------|

| Database | Server Component fetch |

| API | fetch with caching |

| User input | Client state + server action |

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3. Routing Principles

File Conventions

| File | Purpose |

|------|---------|

| page.tsx | Route UI |

| layout.tsx | Shared layout |

| loading.tsx | Loading state |

| error.tsx | Error boundary |

| not-found.tsx | 404 page |

Route Organization

| Pattern | Use |

|---------|-----|

| Route groups (name) | Organize without URL |

| Parallel routes @slot | Multiple same-level pages |

| Intercepting (.) | Modal overlays |

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4. API Routes

Route Handlers

| Method | Use |

|--------|-----|

| GET | Read data |

| POST | Create data |

| PUT/PATCH | Update data |

| DELETE | Remove data |

Best Practices

• Validate input with Zod
• Return proper status codes
• Handle errors gracefully
• Choose Node.js or Edge runtime according to dependency and deployment support; do not assume Node APIs are available on Edge

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5. Performance Principles

Image Optimization

• Use next/image component
• Set priority for above-fold
• Provide blur placeholder
• Use responsive sizes

Bundle Optimization

• Dynamic imports for heavy components
• Route-based code splitting (automatic)
• Analyze with bundle analyzer

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6. Metadata

Static vs Dynamic

| Type | Use |

|------|-----|

| Static export | Fixed metadata |

| generateMetadata | Dynamic per-route |

Essential Tags

• title (50-60 chars)
• description (150-160 chars)
• Open Graph images
• Canonical URL

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7. Caching Strategy

Cache Layers

| Layer | Control |

|-------|---------|

| Request | fetch options |

| Data | revalidate/tags |

| Full route | route config |

Revalidation

| Method | Use |

|--------|-----|

| Time-based | revalidate: 60 |

| On-demand | revalidatePath/Tag |

| No cache | no-store |

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8. Server Actions

Use Cases

• Form submissions
• Data mutations
• Revalidation triggers

Best Practices

• Mark with 'use server'
• Authenticate and authorize each action/handler on the server; exported actions are callable endpoints
• Validate all inputs
• Return typed responses
• Handle errors

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9. Anti-Patterns

| ❌ Don't | ✅ Do |

|----------|-------|

| 'use client' everywhere | Server by default |

| Fetch in client components | Fetch in server |

| Skip loading states | Use loading.tsx |

| Ignore error boundaries | Use error.tsx |

| Large client bundles | Dynamic imports |

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10. Project Structure

app/
├── (marketing)/     # Route group
│   └── page.tsx
├── (dashboard)/
│   ├── layout.tsx   # Dashboard layout
│   └── page.tsx
├── api/
│   └── [resource]/
│       └── route.ts
└── components/
    └── ui/

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> Remember: Server Components are the default for a reason. Start there, add client only when needed.

When to Use

This skill is applicable to execute the workflow or actions described in the overview.

Version scope

Check the installed Next.js version and whether Cache Components is enabled before applying caching advice. The [official caching guide](https://nextjs.org/docs/app/guides/caching) distinguishes these models. Test freshness and invalidation explicitly; never put user-specific secrets or authorization-dependent responses into a shared cache.

Limitations

• Use this skill only when the task clearly matches the scope described above.
• Do not treat the output as a substitute for environment-specific validation, testing, or expert review.
• Stop and ask for clarification if required inputs, permissions, safety boundaries, or success criteria are missing.