reviewing-nextjs-16-patterns

name	reviewing-nextjs-16-patterns
description	Review code for Next.js 16 compliance - security patterns, caching, breaking changes. Use when reviewing Next.js code, preparing for migration, or auditing for violations. Use when this capability is needed.
metadata	{"author":"djankies"}

Next.js 16 Patterns Review

Comprehensive review for Next.js 16 compliance covering security vulnerabilities, caching patterns, breaking changes, and migration readiness.

Review Process

For comprehensive security review patterns, use the reviewing-security skill from the review plugin. For dependency auditing, use the reviewing-dependencies skill from the review plugin.

1. Security Audit

CVE-2025-29927 - Server Action Authentication

Check all Server Actions for proper authentication:

# Find all Server Actions
grep -r "use server" --include="*.ts" --include="*.tsx" --include="*.js" --include="*.jsx"

For each Server Action verify:

• Authentication check at function start
• Authorization validation before data access
• No reliance on client-side validation only
• Proper error handling without leaking sensitive data

Middleware Security

# Find middleware files
find . -name "middleware.ts" -o -name "middleware.js"

Verify:

• Authentication logic present in middleware
• Protected routes defined in config.matcher
• No authentication logic removed in Next.js 16 migration
• Proper redirect handling for unauthorized access

Server Component Data Access

# Find async Server Components
grep -r "export default async function" app/

Check each Server Component:

• Session validation before data queries
• User context verified before personalized data
• No direct database queries without auth checks
• Proper error boundaries for auth failures

2. Caching Patterns

use cache Adoption

# Find fetch calls that should use cache
grep -r "fetch(" --include="*.ts" --include="*.tsx"
# Find functions that should be cached
grep -r "export async function" --include="*.ts"

Verify:

• use cache directive for cacheable functions
• Proper cache tags with cacheTag() for revalidation
• Cache lifecycle control with cacheLife()
• No unstable_cache in new code
• fetch() caching replaced with use cache

Cache Lifecycle Configuration

Check for proper cache profiles:

• cacheLife('seconds') for rapidly changing data
• cacheLife('minutes') for moderate update frequency
• cacheLife('hours') for stable content
• cacheLife('days') for rarely changing data
• cacheLife('weeks') for static content
• Custom profiles defined in next.config.js if needed

Revalidation Strategy

# Find revalidation calls
grep -r "revalidateTag\|revalidatePath" --include="*.ts" --include="*.tsx"

Verify:

• revalidateTag() matches cacheTag() definitions
• revalidatePath() used for page-level invalidation
• No orphaned cache tags
• Proper error handling in revalidation

3. Breaking Changes

Async Request APIs

# Find synchronous API usage
grep -r "cookies()\|headers()\|params\|searchParams" --include="*.ts" --include="*.tsx"

Check for required async usage:

• await cookies() in Server Components/Actions
• await headers() in Server Components/Actions
• await params in page/layout/route components
• await searchParams in page components
• React.use() wrapper in Client Components if needed

Middleware to Proxy Migration

# Check for removed middleware patterns
grep -r "NextResponse.rewrite\|NextResponse.redirect" middleware.ts

Verify migration:

• Simple rewrites moved to next.config.js redirects/rewrites
• Complex logic converted to Middleware Proxies
• Authentication logic preserved
• Header manipulation handled correctly

Route Handler Changes

# Find route handlers
find app -name "route.ts" -o -name "route.js"

Check each route handler:

• Dynamic functions require dynamic = 'force-dynamic'
• No synchronous cookies()/headers() calls
• Proper TypeScript types for request/params
• Error handling updated for new patterns

generateStaticParams Changes

# Find static param generation
grep -r "generateStaticParams" --include="*.ts" --include="*.tsx"

Verify:

• Returns array of param objects (not nested)
• Works with new async params
• Proper TypeScript types
• No deprecated patterns

4. Migration Verification

Dependency Updates

Check package.json:

• next: ^16.0.0 or higher
• react: ^19.0.0 or higher
• react-dom: ^19.0.0 or higher
• @types/react: ^19.0.0 (if using TypeScript)
• @types/react-dom: ^19.0.0 (if using TypeScript)

Configuration Updates

Check next.config.js:

• experimental.dynamicIO enabled if using dynamic APIs
• staleTimes configured if controlling client-side cache
• Custom cacheLife profiles defined if needed
• TypeScript config updated for async params

Build Validation

Run and verify:

npm run build

• No deprecation warnings
• No type errors
• No runtime errors in build
• Static generation works correctly
• Dynamic routes render properly

Runtime Testing

• Authentication flows work correctly
• Protected routes require login
• Server Actions validate permissions
• Cache invalidation triggers updates
• Dynamic content updates appropriately
• Static content serves from cache

Violation Severity

Critical

• Missing authentication in Server Actions (CVE-2025-29927)
• Synchronous cookies()/headers() calls
• Security middleware removed or broken

High

• Missing cache directives on expensive operations
• Incorrect async params usage
• Broken revalidation strategy

Medium

• Using deprecated unstable_cache
• Middleware patterns that should be proxies
• Missing cache lifecycle configuration

Nitpick

• Suboptimal cache profiles
• Missing cache tags for fine-grained invalidation
• Legacy fetch caching patterns

Best Practices

1. Run security audit first - Critical vulnerabilities take priority
2. Group related violations - Fix all async API issues together
3. Test incrementally - Verify each category before moving on
4. Document decisions - Record why certain patterns were chosen
5. Update documentation - Keep project docs current with Next.js 16 patterns

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