Next Best Practices

name: next-best-practices description: "Vercel's authoritative Next.js 15+ patterns covering RSC boundaries, streaming, async patterns, route handlers, metadata, image/font optimization, bundling, hydration errors, parallel routes, and self-hosting. Use when: nextjs, next.js, app router, server components, RSC, next best practices." tags: [nextjs, app-router, server-components, performance]

Next.js Best Practices

Apply these rules when writing or reviewing Next.js code. Maintained by Vercel — the authoritative source for Next.js patterns.

File Conventions

See next-rules.md for:

• Project structure and special files
• Route segments (dynamic, catch-all, groups)
• Parallel and intercepting routes
• Middleware rename in v16 (middleware -> proxy)

RSC Boundaries

Detect invalid React Server Component patterns.

See next-rules.md for:

• Async client component detection (invalid)
• Non-serializable props detection
• Server Action exceptions

Async Patterns

Next.js 15+ async API changes.

See next-rules.md for:

• Async params and searchParams
• Async cookies() and headers()
• Migration codemod

Runtime Selection

See next-rules.md for:

• Default to Node.js runtime
• When Edge runtime is appropriate

Directives

See next-rules.md for:

• 'use client', 'use server' (React)
• 'use cache' (Next.js)

Functions

See next-rules.md for:

• Navigation hooks: useRouter, usePathname, useSearchParams, useParams
• Server functions: cookies, headers, draftMode, after
• Generate functions: generateStaticParams, generateMetadata

Error Handling

See next-rules.md for:

• error.tsx, global-error.tsx, not-found.tsx
• redirect, permanentRedirect, notFound
• forbidden, unauthorized (auth errors)
• unstable_rethrow for catch blocks

Data Patterns

See next-rules.md for:

• Server Components vs Server Actions vs Route Handlers
• Avoiding data waterfalls (Promise.all, Suspense, preload)
• Client component data fetching

Route Handlers

See next-rules.md for:

• route.ts basics
• GET handler conflicts with page.tsx
• Environment behavior (no React DOM)
• When to use vs Server Actions

Metadata & OG Images

See next-rules.md for:

• Static and dynamic metadata
• generateMetadata function
• OG image generation with next/og
• File-based metadata conventions

Image Optimization

See next-rules.md for:

• Always use next/image over <img>
• Remote images configuration
• Responsive sizes attribute
• Blur placeholders
• Priority loading for LCP

Font Optimization

See next-rules.md for:

• next/font setup
• Google Fonts, local fonts
• Tailwind CSS integration
• Preloading subsets

Bundling

See next-rules.md for:

• Server-incompatible packages
• CSS imports (not link tags)
• Polyfills (already included)
• ESM/CommonJS issues
• Bundle analysis

Scripts

See next-rules.md for:

• next/script vs native script tags
• Inline scripts need id
• Loading strategies
• Google Analytics with @next/third-parties

Hydration Errors

See next-rules.md for:

• Common causes (browser APIs, dates, invalid HTML)
• Debugging with error overlay
• Fixes for each cause

Suspense Boundaries

See next-rules.md for:

• CSR bailout with useSearchParams and usePathname
• Which hooks require Suspense boundaries

Parallel & Intercepting Routes

See next-rules.md for:

• Modal patterns with @slot and (.) interceptors
• default.tsx for fallbacks
• Closing modals correctly with router.back()

Self-Hosting

See next-rules.md for:

• output: 'standalone' for Docker
• Cache handlers for multi-instance ISR
• What works vs needs extra setup

Debug Tricks

See next-rules.md for:

• MCP endpoint for AI-assisted debugging
• Rebuild specific routes with --debug-build-paths