nextjs-best-practices

name	nextjs-best-practices
description	Next.js App Router best practices — file conventions, RSC boundaries, data patterns, async APIs, metadata, error handling, route handlers, image/font optimization, bundling. Use when writing, reviewing, or debugging Next.js App Router code.

Next.js Best Practices

Apply these rules when writing or reviewing Next.js code.

Note: Next.js 16 renamed middleware.ts to proxy.ts. Verify proxy.ts support in your version; middleware.ts remains the stable API.

File Conventions

See file-conventions.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 rsc-boundaries.md for:

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

Async Patterns

Next.js 16.1.6+ async API changes.

See async-patterns.md for:

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

Runtime Selection

See runtime-selection.md for:

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

Directives

See directives.md for:

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

Functions

See functions.md for:

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

Error Handling

See error-handling.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 data-patterns.md for:

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

Route Handlers

See route-handlers.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 metadata.md for:

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

Image Optimization

See image.md for:

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

Font Optimization

See font.md for:

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

Bundling

See bundling.md for:

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

Scripts

See scripts.md for:

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

Hydration Errors

See hydration-error.md for:

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

Suspense Boundaries

See suspense-boundaries.md for:

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

Parallel & Intercepting Routes

See parallel-routes.md for:

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

Self-Hosting

See self-hosting.md for:

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

Debug Tricks

See debug-tricks.md for:

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