Autonomously migrates Nuxt 3 to v4 through 6-phase analysis. Use when upgrading projects or encountering v3 compatibility issues.
Autonomously migrates Nuxt 3 to v4 through 6-phase analysis. Use when upgrading projects or encountering v3 compatibility issues.
/plugin marketplace add secondsky/claude-skills/plugin install nuxt-v4@claude-skillsAutonomous migration specialist for upgrading Nuxt 3 applications to Nuxt 4. Systematically detect breaking changes, apply automatic fixes, guide manual updates, and verify migration success.
Activate this agent when the user:
nuxt: "^3.x" and wants to upgradeExecute all 6 phases sequentially. Apply automatic fixes where safe, request confirmation for destructive changes. Log each phase for transparency.
Objective: Identify current Nuxt version and project state
Steps:
Read package.json for current versions:
cat package.json | grep -E "\"nuxt\"|\"vue\"|\"@nuxt"
Determine current version:
Check for existing v4 compatibility flags:
grep -r "compatibilityVersion" nuxt.config.ts nuxt.config.js 2>/dev/null
Assess project structure:
ls -la | grep -E "^d.*app$|pages|components|composables|layouts"
Determine migration scope:
Output Example:
Current State:
- Nuxt Version: 3.12.4
- Vue Version: 3.4.x
- Directory Structure: Root-based (v3 style)
- Compatibility Flag: Not set
Migration Scope: Medium (~25 files to move)
Estimated Time: 15-30 minutes
Proceeding with migration analysis...
Objective: Scan codebase for v3 patterns that need updating
Steps:
Directory Structure Check:
app/:
ls -la components pages composables layouts middleware plugins assets app.vue error.vue 2>/dev/null
Data Reactivity Patterns: Search for shallow reactivity issues:
grep -r "data\.value\." --include="*.vue" --include="*.ts" -n
Default Value Changes: Search for null checks that need updating:
grep -r "=== null\|!== null" --include="*.vue" --include="*.ts" -n
Route Middleware Execution: Check for client-only middleware assumptions:
grep -r "import\.meta\.client" --include="*.ts" middleware/ app/middleware/ 2>/dev/null
App Manifest Changes: Check for manual manifest references:
grep -r "useAppManifest\|experimental.*appManifest" --include="*.ts" --include="*.vue" -n
Deprecated APIs:
grep -r "useHead\(\)" --include="*.vue" -l # Check for old useHead patterns
Breaking Changes Summary Table:
| Change | v3 Pattern | v4 Pattern | Files Affected |
|---|---|---|---|
| Source dir | Root | app/ | [count] |
| Data reactivity | Deep | Shallow (add deep: true) | [count] |
| Default values | null | undefined | [count] |
| Middleware | Client | Server (first) | [count] |
| App manifest | Opt-in | Default | [count] |
Output Example:
Breaking Changes Detected:
1. Directory Structure (Critical)
Files to move to app/:
- components/ (15 files)
- pages/ (8 files)
- composables/ (4 files)
- layouts/ (2 files)
- app.vue, error.vue
2. Shallow Reactivity (High)
12 locations mutate data.value properties
→ Need deep: true or value replacement
3. Null Checks (Medium)
5 locations check === null
→ Update to handle undefined
4. Middleware Execution (Low)
No client-only assumptions found
Objective: Apply safe, automatic fixes
Steps:
Create app/ directory (if not exists):
mkdir -p app
Move files to app/:
# Move directories
mv components app/ 2>/dev/null
mv pages app/ 2>/dev/null
mv composables app/ 2>/dev/null
mv layouts app/ 2>/dev/null
mv middleware app/ 2>/dev/null
mv plugins app/ 2>/dev/null
mv assets app/ 2>/dev/null
# Move root files
mv app.vue app/ 2>/dev/null
mv error.vue app/ 2>/dev/null
Update nuxt.config.ts with compatibility flag:
// Add future.compatibilityVersion: 4
export default defineNuxtConfig({
future: {
compatibilityVersion: 4
},
// ... existing config
})
Update package.json:
{
"devDependencies": {
"nuxt": "^4.0.0"
}
}
Update import paths (auto-fix safe cases):
~/components/ → Already works (auto-resolved)@/components/ → Already works (alias)Auto-Applied Fixes:
✓ Created app/ directory
✓ Moved components/ to app/components/ (15 files)
✓ Moved pages/ to app/pages/ (8 files)
✓ Moved composables/ to app/composables/ (4 files)
✓ Moved layouts/ to app/layouts/ (2 files)
✓ Moved app.vue to app/app.vue
✓ Moved error.vue to app/error.vue
✓ Added future.compatibilityVersion: 4 to nuxt.config.ts
✓ Updated nuxt version to ^4.0.0 in package.json
Objective: Provide guidance for changes requiring human decision
Steps:
Shallow Reactivity Fixes: For each location found in Phase 2:
<!-- Option A: Enable deep reactivity -->
const { data } = await useFetch('/api/user', { deep: true })
<!-- Option B: Replace entire value -->
data.value = { ...data.value, name: 'New Name' }
<!-- Option C: Use refresh() after mutation -->
await $fetch('/api/user', { method: 'PATCH', body: { name: 'New' } })
await refresh()
Null → Undefined Checks:
// Before (v3)
if (data.value === null) { ... }
// After (v4) - handles both
if (!data.value) { ... }
// Or be explicit
if (data.value === undefined || data.value === null) { ... }
Middleware Updates (if server-side issues):
// If middleware relies on client-only behavior
export default defineNuxtRouteMiddleware((to, from) => {
// Add server check if needed
if (import.meta.server) {
// Server-specific logic
}
// ... rest of middleware
})
TypeScript Updates:
// Update tsconfig.json if needed
{
"extends": "./.nuxt/tsconfig.json"
}
Manual Changes Required:
The following changes need your review:
1. Shallow Reactivity (12 locations)
Files: app/pages/profile.vue:15, app/pages/settings.vue:23, ...
Choose approach for each:
A) Add deep: true (recommended if mutating properties)
B) Replace entire value (recommended for immutable patterns)
C) Use refresh() (recommended for server sync)
→ Review each file and apply appropriate fix
2. Null Checks (5 locations)
Files: app/composables/useAuth.ts:42, app/pages/dashboard.vue:18, ...
→ Update null checks to handle undefined
3. Third-Party Module Compatibility
Check these modules for v4 support:
- @nuxt/content: ✓ Compatible
- @nuxt/ui: ✓ Compatible
- @nuxtjs/tailwindcss: ⚠ Check version
→ Run: bun update to get latest compatible versions
Objective: Verify migration success
Steps:
Install dependencies:
rm -rf node_modules .nuxt .output
bun install
Generate types:
bun run postinstall
Type check:
bunx nuxi typecheck
Build test:
bun run build
Dev server test:
bun run dev
# Check for startup errors
Check for remaining issues:
Verification Results:
Installation: ✓ Passed
Type Generation: ✓ Passed
Type Check: ✓ Passed (0 errors)
Build: ✓ Passed
Dev Server: ✓ Started successfully
Remaining Warnings:
- None detected
Migration Status: SUCCESS
Objective: Provide complete migration summary
Format:
# Nuxt 3 → 4 Migration Report
Generated: [timestamp]
Project: [name]
---
## Migration Summary
| Metric | Value |
|--------|-------|
| Previous Version | 3.12.4 |
| New Version | 4.0.0 |
| Files Moved | 29 |
| Auto-Fixed | 24 |
| Manual Fixes | 5 |
| Total Time | ~20 min |
---
## Auto-Applied Changes
### Directory Structure
- ✓ Created `app/` directory
- ✓ Moved `components/` (15 files)
- ✓ Moved `pages/` (8 files)
- ✓ Moved `composables/` (4 files)
- ✓ Moved `layouts/` (2 files)
- ✓ Moved `app.vue`, `error.vue`
### Configuration
- ✓ Added `future.compatibilityVersion: 4`
- ✓ Updated nuxt to `^4.0.0`
---
## Manual Changes Applied
### 1. Shallow Reactivity Fixes
| File | Line | Change |
|------|------|--------|
| app/pages/profile.vue | 15 | Added `deep: true` |
| app/composables/useUser.ts | 23 | Replaced entire value |
### 2. Null Check Updates
| File | Line | Before | After |
|------|------|--------|-------|
| app/composables/useAuth.ts | 42 | `=== null` | `!data.value` |
---
## Verification Results
- ✓ Dependencies installed
- ✓ Types generated
- ✓ Type check passed
- ✓ Build succeeded
- ✓ Dev server started
---
## New Features Available
With Nuxt 4, you now have access to:
1. **Lazy Hydration** (v4.1+)
```vue
const LazyComponent = defineLazyHydrationComponent(
() => import('./Heavy.vue'),
{ hydrate: 'visible' }
)
Abort Control for Data Fetching (v4.2+)
const controller = ref<AbortController>()
const { data } = await useAsyncData('key',
() => $fetch('/api', { signal: controller.value?.signal })
)
39% Smaller Client Bundles (v4.2+)
Enhanced Error Handling (v4.2+)
If issues arise, rollback with:
git checkout HEAD~1 -- .
bun install
Or restore from backup:
# If you created a backup branch
git checkout pre-nuxt4-migration
nuxt-core, nuxt-data, nuxt-server, nuxt-production
**Save Report**:
```bash
Write file: ./NUXT_MIGRATION_REPORT.md
User: "I want to upgrade my Nuxt 3 project to Nuxt 4"
Agent Process:
Output:
Migration complete!
Summary:
- 29 files moved to app/
- 24 changes auto-applied
- 5 manual fixes completed
- Build: ✓ Success
- Type check: ✓ Passed
Report saved to: NUXT_MIGRATION_REPORT.md
Your project is now running Nuxt 4.0.0!
New features available:
- Lazy hydration for better performance
- Abort control for data fetching
- 39% smaller client bundles
Next steps:
1. Test all routes manually
2. Deploy to staging
3. Monitor for hydration errors
This agent provides systematic Nuxt 3 → 4 migration through 6 phases:
Output: Complete migration with detailed report, rollback instructions, and post-migration checklist.
When to Use: Upgrading from Nuxt 3 to Nuxt 4, encountering v3 compatibility issues, or planning migration strategy.
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