Feature-Sliced Design for Nuxt 4+

Official FSD docs: https://feature-sliced.design/ LLM reference: https://feature-sliced.design/llms-full.txt

Core principle

FSD organizes code into layers with a strict dependency rule: each layer can only import from layers below it, never above or sideways. This prevents tangled dependencies — a widget never knows about a page that uses it, a feature never reaches into another feature, and an entity never depends on the UI that displays it.

FSD lives exclusively in src/. The Nuxt app/ directory is the runtime shell — it consumes FSD code from src/ but is not itself organized by FSD. Things like app/composables/, app/middleware/, app/plugins/, and app/layouts/ follow Nuxt conventions, not FSD layers.

FSD layers (all in src/)

Layers are ordered top (most specific) to bottom (most stable). Every layer can only import from layers below it.

pages      ← FSD page slices in src/pages/ — compose widgets, features, entities
widgets    ← Self-contained UI blocks with coupled logic + presentation
features   ← Reusable user interactions — logic is standalone, UI is replaceable
entities   ← Business domain models: types, schemas, base queries, formatters
shared     ← Framework utilities, UI kit, API client, helpers — zero business logic

Layer quick-reference

| Layer | Contains | Does NOT contain | |-------|----------|------------------| | shared | UI kit components, cn(), date/string helpers, API client setup, type utilities | Business logic, domain concepts | | entities | User, Product, Order types, Zod schemas, base useFetch wrappers, model formatters | User actions, interactive features | | features | Auth flow, search logic, cart operations, form submission composables | Entity definitions, layout concerns | | widgets | ProductCard, AppHeader, Sidebar, complete composed sections with own data | Raw entity data access, route logic | | pages | Page slices assembling widgets/features, page-specific data fetching | Reusable pieces (extract when proven) |

---

Nuxt 4+ directory mapping

project-root/
├── app/                          ← Nuxt 4 app directory (runtime shell, NOT FSD)
│   ├── app.vue                   ← Root component
│   ├── pages/                    ← Thin routing shells (see "Thin page pattern")
│   │   ├── index.vue
│   │   └── products/
│   │       ├── index.vue
│   │       └── [id].vue
│   ├── layouts/                  ← Nuxt layouts
│   │   └── default.vue
│   ├── plugins/                  ← Nuxt plugins
│   ├── middleware/               ← Nuxt route middleware
│   └── composables/              ← Nuxt global composables
├── src/                          ← FSD root — all sliced layers live here
│   ├── pages/                    ← FSD page slices (full implementations)
│   │   ├── product-detail/
│   │   │   ├── ui/
│   │   │   │   └── ProductDetailPage.vue
│   │   │   ├── model/
│   │   │   │   └── useProductDetail.ts
│   │   │   └── index.ts
│   │   └── (checkout)/           ← Route group (parentheses)
│   │       ├── _layout/          ← Shared layout for sub-routes
│   │       │   └── CheckoutLayout.vue
│   │       ├── cart/
│   │       │   ├── ui/
│   │       │   └── index.ts
│   │       └── payment/
│   │           ├── ui/
│   │           └── index.ts
│   ├── widgets/                  ← FSD widgets layer
│   │   └── product-card/
│   │       ├── ui/
│   │       │   └── ProductCard.vue
│   │       ├── model/
│   │       │   └── useProductCard.ts
│   │       └── index.ts
│   ├── features/                 ← FSD features layer
│   │   └── add-to-cart/
│   │       ├── ui/
│   │       │   └── AddToCartButton.vue
│   │       ├── model/
│   │       │   └── useAddToCart.ts
│   │       ├── api/
│   │       │   └── mutations.ts
│   │       └── index.ts
│   ├── entities/                 ← FSD entities layer
│   │   └── product/
│   │       ├── ui/
│   │       │   └── ProductPreview.vue
│   │       ├── model/
│   │       │   ├── types.ts
│   │       │   └── schema.ts
│   │       ├── api/
│   │       │   └── queries.ts
│   │       └── index.ts
│   └── shared/                   ← FSD shared layer
│       ├── ui/
│       │   ├── UiButton.vue
│       │   └── UiModal.vue
│       ├── lib/
│       │   ├── format-date.ts
│       │   └── cn.ts
│       ├── api/
│       │   └── client.ts
│       └── config/
│           └── constants.ts
├── server/                       ← Nuxt server routes (outside FSD client layers)
├── public/                       ← Static assets
└── nuxt.config.ts

Key mapping rules

1. src/ is the FSD root. All FSD layers (pages/, widgets/, features/, entities/, shared/) live here.
2. app/ is the Nuxt runtime shell. It follows Nuxt conventions, not FSD. It consumes FSD code from src/ via imports.
3. app/pages/ contains thin routing shells only — they delegate to src/pages/ page slices. See "Thin page pattern" below.
4. server/ is outside FSD entirely. Server routes follow Nuxt server conventions.

---

Thin page pattern

app/pages/*.vue files are routing shells (5–25 lines). They exist solely for Nuxt's file-based routing and delegate all real implementation to FSD page slices in src/pages/.

A thin page:

• Imports the page component from src/pages/<slice>
• Defines definePageMeta({ i18n: { ... } }) for i18n path mappings (if using @nuxtjs/i18n with customRoutes: 'meta')
• Defines definePageMeta() for validation, layout, route key
• Renders the imported page component

Example thin page

<!-- app/pages/products/[id].vue — thin routing shell -->
<script setup lang="ts">
import { ProductDetailPage } from '~~/src/pages/product-detail'

definePageMeta({
  layout: 'default',
  validate: async (route) => /^\d+$/.test(route.params.id as string),
  i18n: {
    paths: {
      cs: '/produkty/[id]',
      en: '/products/[id]',
    },
  },
})
</script>

<template>
  <ProductDetailPage />
</template>

The actual implementation lives in the FSD page slice:

src/pages/product-detail/
  ui/
    ProductDetailPage.vue    ← Full page implementation
  model/
    useProductDetail.ts
  index.ts                   ← Exports ProductDetailPage

---

FSD page slices in src/pages/

src/pages/ contains full FSD page slices — not Nuxt file-based routes. These are regular FSD slices with ui/, model/, api/, and index.ts.

Conventions

• Slice naming: kebab-case matching the domain concept: product-detail/, blog-article-detail/, user-profile/
• Route groups: Parentheses group related sub-routes: (checkout)/cart/, (checkout)/payment/
• Shared layout: _layout/ inside a route group holds layout components shared across sub-routes

Page slice structure

src/pages/product-detail/
  ui/
    ProductDetailPage.vue      ← Main page component
    ProductGallery.vue
    ProductSpecs.vue
  model/
    useProductDetail.ts        ← Page-specific composable
  api/
    queries.ts                 ← Page-specific data fetching
  index.ts                     ← Public API: exports ProductDetailPage

// src/pages/product-detail/index.ts
export { default as ProductDetailPage } from './ui/ProductDetailPage.vue'

---

Imports and aliases

Primary pattern: ~~/src/ prefix

Use Nuxt's ~~/ alias (which resolves to the project root) to import from FSD layers:

// CORRECT — primary import pattern
import { useAuth } from '~~/src/features/auth'
import { type User } from '~~/src/entities/user'
import { UiButton } from '~~/src/shared/ui'
import { ProductDetailPage } from '~~/src/pages/product-detail'

Alternative: custom path aliases

You can optionally configure shorter aliases in nuxt.config.ts:

// nuxt.config.ts
export default defineNuxtConfig({
  alias: {
    '@shared': fileURLToPath(new URL('./src/shared', import.meta.url)),
    '@entities': fileURLToPath(new URL('./src/entities', import.meta.url)),
    '@features': fileURLToPath(new URL('./src/features', import.meta.url)),
    '@widgets': fileURLToPath(new URL('./src/widgets', import.meta.url)),
  },
})

Then use: import { UiButton } from '@shared/ui'. Both patterns are valid — ~~/src/ requires no config, aliases are shorter.

Important: Do NOT rely on Nuxt auto-imports for cross-layer dependencies. Always use explicit imports through the slice's public API (index.ts). This keeps dependencies visible and enforceable.

// CORRECT — explicit import via public API
import { useAuth } from '~~/src/features/auth'

// WRONG — deep import bypassing public API
import { useAuth } from '~~/src/features/auth/model/useAuth'

Nuxt auto-imports are acceptable only for:

• Vue/Nuxt built-ins (ref, computed, useFetch, useRoute, navigateTo, etc.)
• Global app-layer composables in app/composables/

---

TypeScript configuration

Since src/ lives outside the Nuxt app/ directory, you must explicitly include it in the TypeScript config:

// nuxt.config.ts
export default defineNuxtConfig({
  typescript: {
    tsConfig: {
      include: ['../src/**/*'],
    },
    sharedTsConfig: {
      include: ['../src/**/*'],
    },
    nodeTsConfig: {
      include: ['../src/**/*'],
    },
  },
})

This ensures all three Nuxt-generated tsconfigs (client, shared, server) include type-checking and auto-completion for FSD code in src/.

---

Slices and segments

A slice is a subfolder inside a layer, named after a business domain concept:

• src/features/auth, src/entities/user, src/widgets/product-card

A segment groups code by technical role inside a slice:

src/features/auth/
  ui/          ← Vue components
  model/       ← Composables, stores (Pinia), state, types
  api/         ← Data fetching (useFetch, $fetch, query wrappers)
  lib/         ← Helpers specific to this slice
  config/      ← Constants, feature flags
  index.ts     ← Public API (REQUIRED)

Naming conventions

• kebab-case everywhere: user-profile, add-to-cart, product-card
• Domain-first names, NOT technical: auth not use-auth-hook, product not product-helpers
• Vue components: PascalCase filenames matching component name: LoginForm.vue, ProductCard.vue
• Composables: camelCase with use prefix: useAuth.ts, useProductSearch.ts

---

Public API

Every slice must expose an index.ts. External code imports only from index.ts.

// src/features/auth/index.ts
export { default as LoginForm } from './ui/LoginForm.vue'
export { useAuth } from './model/useAuth'
export { useProvideAuth } from './model/useAuth'
export type { AuthUser, AuthCredentials } from './model/types'

Deep imports are forbidden between slices:

// WRONG
import { useAuth } from '~~/src/features/auth/model/useAuth'

// CORRECT
import { useAuth } from '~~/src/features/auth'

Within-slice relative imports are fine:

// Inside src/features/auth/ui/LoginForm.vue
import { useAuth } from '../model/useAuth'

---

Pages-first workflow

Start everything in src/pages/. Extract only when reuse is proven.

New functionality needed
        │
        v
  Build inside src/pages/<slice>/
        │
        v
  Used in a 2nd place?
     NO --> Keep in src/pages/
     YES
        │
        v
  Duplicate it (2 copies is acceptable)
        │
        v
  Used in a 3rd place?
     NO --> Keep duplicated
     YES
        │
        v
  Extract. Ask: "Is this logic always tied to THIS specific UI?"
     YES --> Widget (logic + UI coupled)
      NO --> Feature (logic reusable, UI replaceable)
             or Entity (pure domain data, no user action)

Rule: Extract when you have evidence (3+ usages), not a prediction. Premature extraction creates unnecessary abstraction.

---

Widget vs Feature decision

The critical question: "Can the logic be used WITHOUT this specific UI?"

Widget — logic and UI are inseparable

• Always rendered as a unit
• Contains its own data fetching and state
• Reused across 2+ pages but always as a whole block

src/widgets/job-list/
  ui/
    JobList.vue          ← Fetches data, renders list, handles pagination
    JobListItem.vue      ← Presentational sub-component
  model/
    useJobList.ts        ← Encapsulated composable, not exported alone
  index.ts               ← Exports only <JobList />

Feature — logic is standalone

• Composable works with any UI
• Default UI is provided but replaceable
• Logic can be used headlessly

src/features/search/
  model/
    useSearch.ts         ← Works standalone, any UI can consume it
  ui/
    SearchBar.vue        ← Default UI, receives state via props/inject
  index.ts               ← Exports both useSearch and SearchBar

Quick decision table

| Module | Widget or Feature? | Why | |--------|-------------------|-----| | Search with debounced results | Feature | useSearch powers different UIs | | Infinite scroll product list | Widget | Fetch + render always together | | Auth login form | Feature | useAuth reusable in modal, page, drawer | | Navigation sidebar | Widget | Nav items + layout always coupled | | Like/bookmark button | Feature | useLike works standalone | | Dashboard stats panel | Widget | Chart + data always together |

---

State management placement

All state lives in the model/ segment of the relevant slice:

| Pattern | When to use | Placement | |---------|------------|-----------| | Simple composable (useState) | Shared state within a feature/entity, SSR-safe | src/features/auth/model/useAuth.ts | | Provider/Inject (createInjectionState) | State scoped to a component subtree | src/features/cart/model/useCart.ts | | Pinia store | Global state, devtools, persistence, complex actions | src/entities/user/model/store.ts |

Provider/Inject pattern

Use createInjectionState from @vueuse/core for scoped state. Always export a throwing variant so consumers get a clear error if the provider is missing:

// src/features/auth/model/useAuth.ts
import { createInjectionState } from '@vueuse/core'

const [useProvideAuth, useAuthRaw] = createInjectionState(() => {
  const user = ref<User | null>(null)
  return { user }
})

export { useProvideAuth }

export function useAuth() {
  const state = useAuthRaw()
  if (!state) throw new Error('useAuth must be used within AuthProvider')
  return state
}

Data fetching placement

| What | Where | Example path | |------|-------|-------------| | Base queries (read) | Entity api/ segment | src/entities/product/api/queries.ts | | Mutations (write) | Feature api/ segment | src/features/add-to-cart/api/mutations.ts | | Page-specific fetching | Page slice api/ or inline | src/pages/product-detail/api/queries.ts |

---

Import rules (strict)

Layer imports — only downward (within src/)

pages     can import from → widgets, features, entities, shared
widgets   can import from → features, entities, shared
features  can import from → entities, shared
entities  can import from → shared
shared    can import from → (nothing — only external packages)

app/ (Nuxt shell) can import from any FSD layer in src/.

Same-layer isolation

Slices within the same layer cannot import from each other:

// WRONG — features/auth importing from features/profile
import { useProfile } from '~~/src/features/profile'

// CORRECT — extract shared concept to entities or shared
import { type User } from '~~/src/entities/user'

Cross-entity references (@x notation)

When entities have legitimate business relationships, use explicit @x cross-references:

// src/entities/order/ui/OrderCard.vue
import { UserAvatar } from '~~/src/entities/user/@x/order'

The @x/<consumer> folder is a controlled cross-import API. Use sparingly.

---

Cross-slice communication patterns

When slices on the same layer need to coordinate:

1. Extract to a lower layer — if two features share a concept, move it to entities or shared
2. Event-based communication — use a shared event bus (mitt) or Pinia store for loose coupling
3. Composition at a higher layer — let a page or widget compose multiple features together

---

Nuxt app/ directory (not FSD)

Everything in app/ follows Nuxt conventions, not FSD. These files consume FSD code from src/ but are not themselves organized into FSD layers:

| Nuxt directory | Role | Relation to FSD | |----------------|------|-----------------| | app/pages/ | Thin routing shells | Imports page components from src/pages/ | | app/layouts/ | Nuxt layouts | May import widgets from src/widgets/ | | app/middleware/ | Route middleware | May import composables from src/features/ or src/entities/ | | app/plugins/ | Global setup | May import from any src/ layer | | app/composables/ | Global composables | Only truly app-wide concerns, not FSD-sliced code | | server/ | Server routes | Entirely outside FSD, follows Nuxt server conventions |

---

Shared layer structure

The shared layer has no slices — only segments:

src/shared/
  ui/               ← Generic UI components: buttons, modals, inputs, cards
  lib/              ← Utility functions: formatDate, cn(), debounce
  api/              ← API client setup, interceptors, base fetch wrapper
  config/           ← App-wide constants, env helpers, route names
  types/            ← Shared TypeScript utility types

Each segment can have its own index.ts for cleaner imports.

---

Scaffolding a new slice

src/features/bookmark/
  ui/
    BookmarkButton.vue
  model/
    useBookmark.ts
    types.ts
  api/
    mutations.ts
  index.ts              ← Public API (REQUIRED)

Only create segments you actually need. An entity with only types needs only model/ and index.ts.

---

Common mistakes

1. Putting FSD layers inside app/

Wrong: app/features/, app/entities/, app/widgets/, app/shared/. Right: FSD layers live in src/. Only app/pages/ (thin shells), app/layouts/, app/plugins/, app/middleware/, app/composables/ go in app/.

2. Fat page routes

Wrong: Putting full page implementations in app/pages/products/[id].vue (200+ lines). Right: app/pages/ files are thin routing shells (5–25 lines) that import from src/pages/.

3. Premature extraction

Wrong: Creating src/features/fancy-button because "it might be reused." Right: Keep in src/pages/ until 3 actual usages prove the need.

4. Wrong layer

Wrong: Putting useProductSearch (standalone logic) in a widget. Right: Ask "can this logic work without THIS specific UI?" — yes means Feature.

5. Missing public API

Wrong: import { x } from '~~/src/features/auth/model/internal' Right: All exports go through index.ts.

6. Upward imports

Wrong: src/entities/user importing from src/features/auth. Right: Dependency flows only downward — entities never reference features.

7. Same-layer cross-imports

Wrong: src/features/profile importing from src/features/auth. Right: Extract shared concept to entities/ or use events.

8. Business logic in shared

Wrong: src/shared/lib/useAuth.ts, src/shared/lib/useProductSearch.ts. Right: Shared is for generic utilities only — zero business logic.

9. Relying on Nuxt auto-imports for FSD layers

Wrong: Expecting useAuth() to auto-resolve from src/features/auth/model/. Right: Use explicit imports via ~~/src/features/auth public API.

10. Applying FSD outside src/

Wrong: Organizing app/composables/, app/middleware/, or server/ into FSD layers. Right: FSD lives exclusively in src/. Everything else (app/, server/) follows Nuxt conventions.

---

Checklist for new code

Before writing or reviewing code, verify:

• [ ] Which layer does this belong to? (Use the decision tree)
• [ ] Does the slice have an index.ts public API?
• [ ] Are all cross-slice imports going through index.ts?
• [ ] Am I importing only from layers below?
• [ ] Are imports using ~~/src/ prefix (or configured aliases)?
• [ ] Is app/pages/*.vue a thin routing shell (<25 lines)?
• [ ] Widget or Feature? (Asked: "can logic exist without this UI?")
• [ ] Is extraction proven (3+ usages) or premature?
• [ ] Is all FSD-structured code in src/, not in app/ or server/?
• [ ] Does app/ only contain Nuxt runtime concerns (thin pages, layouts, plugins, middleware)?

---

Migration strategy

For existing Nuxt projects adopting FSD with src/ root:

| Code | Approach | |------|----------| | New modules | Always follow FSD in src/ | | Existing app/components/ | Migrate to src/shared/ui/ or appropriate slice ui/ segment | | Existing app/composables/ | Classify into feature/entity model/ in src/ or keep in app/composables/ if truly global | | Existing app/utils/ | Move to src/shared/lib/ | | Existing app/stores/ | Move to entity/feature model/ segments in src/ | | Existing fat pages | Split into thin shell in app/pages/ + page slice in src/pages/ |

Steps:

1. Create src/ directory with FSD layer subdirectories
2. Add typescript includes (tsConfig, sharedTsConfig, nodeTsConfig) to nuxt.config.ts
3. Start all new code in FSD structure under src/
4. Migrate existing code slice-by-slice when touched
5. Convert fat pages to thin routing shells + src/pages/ slices
6. Update imports to use ~~/src/ and public APIs
7. Remove old directories once empty