nextjs

# Next.js App Router - Production Patterns

**Version**: Next.js 16.1.1
**React Version**: 19.2.3
**Node.js**: 20.9+
**Last Verified**: 2026-01-09

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## Table of Contents

1. [When to Use This Skill](#when-to-use-this-skill)
2. [When NOT to Use This Skill](#when-not-to-use-this-skill)
3. [Security Advisories (December 2025)](#security-advisories-december-2025)
4. [Next.js 16.1 Updates](#nextjs-161-updates-december-2025)
5. [Next.js 16 Breaking Changes](#nextjs-16-breaking-changes)
6. [Cache Components & Caching APIs](#cache-components--caching-apis)
7. [Route Handlers (Next.js 16 Updates)](#route-handlers-nextjs-16-updates)
8. [Proxy vs Middleware](#proxy-vs-middleware)
9. [Parallel Routes - default.js Required](#parallel-routes---defaultjs-required-breaking)
10. [React 19.2 Features](#react-192-features)
11. [Turbopack (Stable in Next.js 16)](#turbopack-stable-in-nextjs-16)
12. [Common Errors & Solutions](#common-errors--solutions)
13. [Templates & Resources](#templates--resources)

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## When to Use This Skill

**Focus**: Next.js 16 breaking changes and knowledge gaps (December 2024+).

Use this skill when you need:

- **Next.js 16 breaking changes** (async params, proxy.ts, parallel routes default.js, removed features)
- **Cache Components** with `"use cache"` directive (NEW in Next.js 16)
- **New caching APIs**: `revalidateTag()`, `updateTag()`, `refresh()` (Updated in Next.js 16)
- **Migration from Next.js 15 to 16** (avoid breaking change errors)
- **Async route params** (`params`, `searchParams`, `cookies()`, `headers()` now async)
- **Parallel routes with default.js** (REQUIRED in Next.js 16)
- **React 19.2 features** (View Transitions, `useEffectEvent()`, React Compiler)
- **Turbopack** (stable and default in Next.js 16)
- **Image defaults changed** (TTL, sizes, qualities in Next.js 16)
- **Error prevention** (25 documented Next.js 16 errors with solutions)

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## When NOT to Use This Skill

Do NOT use this skill for:

- **Cloudflare Workers deployme