Verdicts

Vitest 5.0.0 for functions and components, Playwright 1.63.0 for the flows that make you money. Vitest reuses your Vite config so path aliases and TypeScript work without a second build, and Playwright drives real Chromium, Firefox, and WebKit with traces you can open after a CI failure. Skip a unit test for a server component that only awaits a query and reads props; test the query and the page instead.

Start with server components and no client cache at all: fetch in the server component, mutate in a server action, and let the framework revalidate. Add TanStack Query 5.102.8 only for the screens that need polling, infinite scroll, optimistic updates, or offline retry, and keep the rest on the server.

next-intl 4.14.2. It is built for the App Router specifically, so the locale reaches server components, metadata, and route handlers without a client provider wrapping the tree, and ICU message syntax covers plurals and dates. Lingui 6.6.0 is the alternative worth knowing: macros extract to PO files, the runtime is around 2 kB, and it documents React Server Component support.

Coolify v4.3.18 if you want a UI: Apache-2.0, 61k stars, and it drives Docker over SSH so the same install manages several servers. Plain Docker Swarm on Docker 29.8.0 if you would rather own the compose file: `docker stack deploy` plus a Caddy or Traefik service is roughly eighty lines and nothing sits between you and the daemon. Dokploy v0.30.5 is the same idea as Coolify on Swarm, with a smaller team behind it.

Next.js 16.3.4 if the app is mostly logged-in screens: server components, the largest hiring pool, and Turbopack on by default for both dev and build. Astro 7.3.1 if most pages are content and only a few islands are interactive, because it ships no JS for the rest. SvelteKit 2.70.3 is the smallest runtime of the three, but v3 is in prerelease and rewrites the adapter API, so custom adapters will need work.

Fumadocs 16.15.8 if the docs live inside an existing Next.js app, because it is Next.js components rather than a separate site and you share the layout, the fonts, and the deploy. Starlight 0.42.0 if the docs are their own site: Astro ships almost no JS, and i18n, search, and the sidebar are configuration. Docusaurus 3.10.2 is the safe institutional choice with the deepest plugin and versioning story.

Better Auth. You own the users table in your own Postgres, the organization and api-key plugins cover teams and keys without a second vendor, and there is no per-monthly-active-user bill when you grow.