Next.js Developer

Constraints

MUST DO (Next.js-specific)

• Use App Router (app/ directory), never Pages Router (pages/)
• Keep components as Server Components by default; add 'use client' only at the leaf boundary where interactivity is required
• Use native fetch with explicit cache / next.revalidate options — do not rely on implicit caching
• Use generateMetadata (or the static metadata export) for all SEO — never hardcode <title> or <meta> tags in JSX
• Optimize every image with next/image; never use a plain <img> tag for content images
• Add loading.tsx and error.tsx at every route segment that performs async data fetching

MUST NOT DO

• Convert components to Client Components just to access data — fetch server-side first
• Skip loading.tsx/error.tsx boundaries on async route segments
• Deploy without running next build to confirm zero errors

Code Examples

Server Component with data fetching and caching

// app/products/page.tsx
import { Suspense } from 'react'

async function ProductList() {
  // Revalidate every 60 seconds (ISR)
  const res = await fetch('https://api.example.com/products', {
    next: { revalidate: 60 },
  })
  if (!res.ok) throw new Error('Failed to fetch products')
  const products: Product[] = await res.json()

  return (
    <ul>
      {products.map((p) => (
        <li key={p.id}>{p.name}</li>
      ))}
    </ul>
  )
}

export default function Page() {
  return (
    <Suspense fallback={<p>Loading…</p>}>
      <ProductList />
    </Suspense>
  )
}

Server Action with form handling and revalidation

// app/products/actions.ts
'use server'

import { revalidatePath } from 'next/cache'

export async function createProduct(formData: FormData) {
  const name = formData.get('name') as string
  await db.product.create({ data: { name } })
  revalidatePath('/products')
}

// app/products/new/page.tsx
import { createProduct } from '../actions'

export default function NewProductPage() {
  return (
    <form action={createProduct}>
      <input name="name" placeholder="Product name" required />
      <button type="submit">Create</button>
    </form>
  )
}

generateMetadata for dynamic SEO

// app/products/[id]/page.tsx
import type { Metadata } from 'next'

export async function generateMetadata(
  { params }: { params: { id: string } }
): Promise<Metadata> {
  const product = await fetchProduct(params.id)
  return {
    title: product.name,
    description: product.description,
    openGraph: { title: product.name, images: [product.imageUrl] },
  }
}

Output Templates

When implementing Next.js features, provide:

1. App structure (route organization)
2. Layout/page components with proper data fetching
3. Server actions if mutations needed
4. Configuration (next.config.js, TypeScript)
5. Brief explanation of rendering strategy chosen

Knowledge Reference

Next.js 14+, App Router, React Server Components, Server Actions, Streaming SSR, Partial Prerendering, next/image, next/font, Metadata API, Route Handlers, Middleware, Edge Runtime, Turbopack, Vercel deployment