Nextjs App Architecture

Next.js App Architecture

A workflow for building and auditing Next.js 16+ App Router apps so they follow one consistent, feature-sliced RSC architecture like next-beats.

Follow the workflow below step by step — it produces the invariants by construction. Load the reference a step names for the decision it depends on. Get framework mechanics (API signatures, config options, hook contracts) from the linked docs — don't restate or improvise them.

Prerequisite

Before changing a Next.js app, make sure the project is set up for AI agents to read version-matched docs. Follow the AI Coding Agents guide: prefer the project's AGENTS.md / bundled docs, and create or refresh them when missing. Then use this skill for architecture decisions.

Architecture target

Build pages that describe the loading experience, not pages that act like route loaders:

• app/**/page.tsx and layout.tsx are synchronous composition surfaces: static chrome, section headings, <Suspense> boundaries, error boundaries, and transition wrappers.
• Feature components own their reads on the server. They receive minimal stable inputs (id, slug, handle, parsed filter values) or already-fetched records, never raw params / searchParams.
• Queries and actions live in the feature folder. Components import queries; client leaves import actions directly.
• When server tags and client query keys describe the same feature data, a pure feature-local cache contract owns those identities.
• Skeletons mirror the component tree and live beside the component they represent.

Invariants (what every change must satisfy)

The non-negotiables. The workflow produces them; the final check verifies them.

1. Pages compose, they never fetch. A page/layout imports feature components and places <Suspense>. No queries, no domain logic, no route-specific components defined inline.
2. Pages stay synchronous. Use params.then() / searchParams.then(), never await params at the top — so chrome paints into the static shell and only data-dependent sections suspend.
3. Feature components receive IDs, not route props. Resolve params / searchParams at the page boundary and pass plain values (id, slug, query) into features.
4. Async server component is the default. 'use client' only for hooks, event handlers, or browser APIs — and only on leaves, never on parents of server content.
5. The page owns the Suspense boundary; the feature owns the skeleton. Features never pre-wrap themselves in <Suspense>.
6. Skeletons live in the same file as the component, exported alongside it, defined at the end. Feed and FeedSkeleton are siblings.
7. Queries live in <domain>-queries.ts (import 'server-only'); actions live in <domain>-actions.ts ('use server'). The file name matches the folder, even for sub-concepts.
8. One feature folder per real domain noun. Sub-concepts (favorite, like, vote, bookmark, search) fold into the parent feature, never their own folder.
9. Client components import actions directly — never receive a server action as a prop just to call it.
10. Feature-local cache coordination stays with its domain. Put pure tags/keys in <domain>-cache.ts, client query definitions in <domain>-query-options.ts, hook wrappers in hooks/use-*.ts, and tiny client leaves in components/; promote support code only after real cross-feature reuse.

Workflow

Run these in order for build-from-scratch, feature work, or audits. Each step names the reference to consult and the check it must pass.

1. Choose mode.
   • Build from scratch: sketch routes, real domain nouns, static shell, and expected loading groups before writing code.
   • Audit/refactor: scan current app/ pages first; list every async page, page-level query import, route prop leak, missing Suspense boundary, and feature folder mismatch. → references/example.md for the target shape; references/feature-folders.md for placement. ✓ You know whether you are creating the architecture or converting loader-shaped code into it.
2. Place the work. Decide the feature folder before writing anything. → references/feature-folders.md (decision tree + merge rules). ✓ A real domain, or folded into the right parent.
3. Write the query and, when a client cache shares its data, the cache contract. Put server reads in <domain>-queries.ts with import 'server-only'; keep shared tag/key identities in a pure <domain>-cache.ts. → references/queries-actions.md; for SWR/TanStack Query → references/single-page-applications.md; with cacheComponents: true, also → references/cache-components.md. ✓ Cache identities are defined once; server reads are server-only, cached/tagged/lifetimed under Cache Components, and return domain types rather than ORM rows.
4. Write the action (if there's a mutation). features/<domain>/<domain>-actions.ts, 'use server' at the top. → references/queries-actions.md. ✓ Re-checks auth, validates input, invalidates matching cache tags under Cache Components (refresh() only for justified dynamic reads), returns a discriminated union.
5. Build the component + skeleton. features/<domain>/components/<name>.tsx: an async server component that awaits its own query from minimal props; 'use client' only on interactive leaves. → references/components.md; for a client data library or strict-SPA/CSR feature → references/single-page-applications.md. ✓ Component receives IDs/handles/parsed filters or already-resolved records, not params; skeleton is a sibling export at the end; no alias skeleton wrappers.
6. Compose the page. app/<route>/page.tsx: synchronous, params.then(), place <Suspense fallback={<NameSkeleton />}><Name /></Suspense>, and wrap fallible sections in an error boundary. → references/pages-suspense.md. ✓ The page only composes; the boundary lives here, not in the feature; route props are resolved to plain values before reaching feature components.
7. Add interaction (if any): optimistic updates, pending state, toasts, confirmation. → references/ux-patterns.md. ✓ Feedback isn't doubled; destructive actions confirm; feature-owned client coordination stays with that feature instead of leaking into unrelated domains.
8. Verify against the checklist below before declaring done.