next-best-practices

SKILL.md

Next.js Best Practices

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

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 15+ 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