Next.js

Official docs

Topic	URL
App Router	https://nextjs.org/docs/app
Data fetching	https://nextjs.org/docs/app/building-your-application/data-fetching
Caching	https://nextjs.org/docs/app/building-your-application/caching
Route Handlers	https://nextjs.org/docs/app/building-your-application/routing/route-handlers

App Router default — prefer app/ over pages/ unless repo is Pages-only.
Server vs client — 'use client' only when hooks, browser APIs, or event handlers require it.
Caching — read existing revalidate, fetch cache, and unstable_cache patterns before changing behavior.
Metadata — export metadata or generateMetadata on public routes; update sitemap.ts for new slugs.
Do not invent API — Context7 MCP for @next/* syntax; avoid hallucinated Next 15 config flags.