| name | nextjs16-skills |
| description | Key facts and links for Next.js 16. Use for planning, writing, and troubleshooting Next.js 16 changes. |
Triggers
- nextjs
- next.js
- next
- app router
- server component
- ssr
- ssg
- vercel
- next 16
- pages router
- middleware
- next api
Links
Upgrade
npx @next/codemod@canary upgrade latest
npm install next@latest react@latest react-dom@latest
npx create-next-app@latest
Codemod covers (high-level): moves Turbopack config, migrates next lint → ESLint CLI, migrates middleware → proxy, removes some unstable_ prefixes, removes route-level experimental_ppr.
TypeScript: also upgrade @types/react and @types/react-dom.
What’s New (v16)
- Cache Components: opt-in caching via the
"use cache" directive; evolves/absorbs PPR.
- Next.js DevTools MCP: Model Context Protocol integration for AI-assisted debugging.
proxy.ts: clearer network boundary; middleware.ts deprecated for most use.- Better logs/metrics: more detailed
next dev and build timing output.
Performance / DX
- Turbopack: stable; default bundler (opt out with
next dev --webpack, next build --webpack).
- If you have a custom
webpack config, next build may fail (to prevent misconfiguration). Fix by migrating config, using next build --webpack, or using Turbopack and removing/ignoring the webpack config.
- Turbopack config moved:
experimental.turbopack → top-level turbopack in next.config.*.
- Turbopack migration gotchas:
- Sass imports: remove the Webpack-only
~ prefix (e.g. @import 'bootstrap/...';).
- Browser bundles must not import Node built-ins (e.g.
fs). If unavoidable, use turbopack.resolveAlias as a stopgap.
- Turbopack filesystem cache (dev, beta):
experimental.turbopackFileSystemCacheForDev: true.
- React Compiler support: stable opt-in via
reactCompiler: true (expect higher build/compile cost).
- Build Adapters API: alpha (custom build adapters).
- Routing/prefetching rewrite: layout deduplication + incremental prefetching.
Caching APIs (key signatures)
revalidateTag(tag, profile) now requires a cacheLife profile (or { expire }) for SWR behavior.updateTag(tag) (Server Actions only): read-your-writes semantics.refresh() (Server Actions only): refresh uncached data; does not mutate cache.cacheLife and cacheTag are stable (no unstable_ prefix).
Requirements (v16)
- Node.js: 20.9+ (Node 18 not supported)
- TypeScript: 5.1+
- Browsers: Chrome/Edge/Firefox 111+, Safari 16.4+
Breaking / Behavior Changes (high-impact)
- Async Request APIs: sync access removed. Use
await params, await searchParams, await cookies(), await headers(), await draftMode().
- Tip (TypeScript):
npx next typegen can generate helpers like PageProps, LayoutProps, RouteContext to migrate params/searchParams types safely.
- Metadata images:
opengraph-image, twitter-image, icon, apple-icon now receive params (and id) as Promises in the image function.
- Sitemaps:
sitemap({ id }) now receives id as a Promise when using generateSitemaps.
- Parallel routes: slots require explicit
default.js.
next/image defaults changed (cache TTL, sizes/qualities); local src with query strings requires images.localPatterns.
Other notable behavior changes:
next dev and next build use separate output dirs (next dev → .next/dev) and a lockfile prevents concurrent instances.- Scroll behavior: Next.js no longer overrides global
scroll-behavior: smooth during navigations; add data-scroll-behavior="smooth" on <html> to restore the previous override behavior.
- ESLint:
@next/eslint-plugin-next defaults to ESLint Flat Config; legacy .eslintrc projects may need migration.
Removed / Deprecated (high-level)
- Removed: AMP support;
next lint (use ESLint/Biome directly); eslint option in next.config.*; serverRuntimeConfig/publicRuntimeConfig (use env vars); experimental.ppr + route-level experimental_ppr; unstable_rootParams.
- Deprecated:
middleware.ts filename (prefer proxy.ts); next/legacy/image; images.domains (prefer images.remotePatterns); revalidateTag(tag) single-arg form.
proxy.ts note: proxy runs on nodejs only; Edge runtime is not supported in proxy. Keep middleware.ts if you must stay on Edge.- Config rename example:
skipMiddlewareUrlNormalize → skipProxyUrlNormalize.
Verify
- The Next.js version targeted is named explicitly (e.g., 'Next 16') and the change does not silently rely on features from a different major
next build (or the project's equivalent) was run and completed without errors; the build output / route table is captured- Server components vs client components were chosen deliberately for each new file; the choice is justified in a comment or PR note
next dev was loaded and the touched routes were rendered without console warnings or hydration mismatches- Caching/revalidation behavior (fetch options,
revalidate, dynamic) is set explicitly on new data fetches, not left to defaults
- Type-check and lint (
tsc --noEmit, next lint) pass on the changed files; output is in the transcript
