Next.js Best Practices

Comprehensive performance optimization and best practices for Next.js applications, designed for AI agents and LLMs working with Next.js code.

When to Activate This Skill

Use this skill when the task involves:

Writing Next.js Code

• Creating Server Components or Client Components
• Implementing Server Actions with "use server"
• Writing API route handlers
• Setting up data fetching in RSC (React Server Components)
• Implementing Suspense boundaries
• Using Next.js-specific APIs (headers(), cookies(), after())

Refactoring Next.js Code

• Optimizing server-side data fetching
• Reducing RSC serialization overhead
• Converting sequential to parallel operations
• Restructuring component composition for better performance
• Migrating between Server and Client Components

Performance Optimization

• Eliminating server-side waterfalls
• Reducing response times in API routes and Server Actions
• Minimizing data transfer at RSC boundaries
• Implementing request deduplication with React.cache()
• Using after() for non-blocking operations

Next.js-Specific Issues

• Authentication/authorization in Server Actions
• RSC serialization duplication problems
• Import optimization (barrel file issues)
• Server vs Client Component decision-making
• Parallel data fetching patterns

Code Review

• Reviewing Next.js code for performance anti-patterns
• Identifying security issues in Server Actions
• Checking proper Server/Client Component boundaries
• Ensuring proper authentication patterns
• Validating Suspense boundary placement

When NOT to Use This Skill

Do not activate for:

• React-specific optimizations (use accelint-react-best-practices skill)
• Build configuration (webpack, turbopack) unless Next.js-specific
• General TypeScript/JavaScript questions (use accelint-ts-best-practices skill)
• Deployment/hosting configuration
• Testing setup (use accelint-ts-testing skill)

Example Trigger Phrases

This skill should activate when users say things like:

Performance Issues:

• "This Next.js API route is slow"
• "My Server Component is blocking the entire page"
• "Optimize this Server Action"
• "The page takes forever to load data"
• "There's a waterfall in my data fetching"

Security Issues:

• "Add authentication to this Server Action"
• "This Server Action needs authorization"
• "Secure this API route"
• "Validate input in this Server Action"

Debugging Issues:

• "Why is my RSC props so large?"
• "This data is being duplicated in the HTML"
• "My imports are slow in development"
• "Should this be a Server or Client Component?"

Code Review:

• "Review this Next.js code for performance issues"
• "Is this Server Action secure?"
• "Can you optimize this data fetching?"
• "Check if this component should be server or client"

Refactoring:

• "Parallelize these data fetches"
• "Reduce the serialization size"
• "Convert this to use Suspense"
• "Optimize this barrel import"

How to Use

This skill uses a progressive disclosure structure to minimize context usage:

1. Start with the Overview (AGENTS.md)

Read AGENTS.md for a concise overview of all rules with one-line summaries.

2. Load Specific Rules as Needed

When you identify a relevant optimization, load the corresponding reference file for detailed implementation guidance:

General Patterns:

• prevent-waterfall-chains.md (1.1)
• parallelize-independent-operations.md (1.2)
• strategic-suspense-boundaries.md (1.3)

Server-Side Performance:

• server-actions-security.md (2.1)
• avoid-duplicate-serialization.md (2.2)
• minimize-serialization.md (2.3)
• parallel-data-fetching.md (2.4)
• react-cache-deduplication.md (2.5)
• use-after-non-blocking.md (2.6)

Misc:

• avoid-barrel-imports.md (3.1)
• server-vs-client-component.md (3.2)

Quick References:

• quick-checklist.md
• compound-patterns.md

Automation Scripts:

• scripts/ - Helper scripts to detect anti-patterns

3. Apply the Pattern

Each reference file contains:

• ❌ Incorrect examples showing the anti-pattern
• ✅ Correct examples showing the optimal implementation
• Explanations of why the pattern matters
• Performance impact metrics
• Related patterns and references

4. Use the Report Template

When this skill is invoked for Next.js code review, use the standardized report format:

Template: assets/output-report-template.md

The report format provides:

• Executive Summary with impact assessment
• Severity levels (Critical, High, Medium, Low) for prioritization
• Impact analysis (performance, security, data transfer, maintainability)
• Categorization (Server Actions, RSC Serialization, Data Fetching, Component Architecture)
• Pattern references linking to detailed guidance in references/
• Summary table for tracking all issues

When to use the report template:

• Skill invoked directly via /accelint-nextjs-best-practices <path>
• User asks to "review Next.js code" or "audit Next.js app" across file(s), invoking skill implicitly

When NOT to use the report template:

• User asks to "fix this Server Action" (direct implementation)
• User asks "what's wrong with this code?" (answer the question)
• User requests specific fixes (apply fixes directly without formal report)

Examples

Example 1: Optimizing Server Action Security

Task: "Add authentication to this Server Action"

Approach:

1. Read AGENTS.md overview
2. Identify issue: Server Action needs authentication
3. Load server-actions-security.md
4. Apply authentication pattern with validation

Example 2: Eliminating Waterfalls

Task: "This page loads slowly with multiple fetches"

Approach:

1. Read AGENTS.md overview
2. Identify issue: Sequential data fetching
3. Load prevent-waterfall-chains.md and parallelize-independent-operations.md
4. Start operations immediately and use Promise.allSettled()

Example 3: Reducing Serialization

Task: "The HTML response is huge with user data"

Approach:

1. Read AGENTS.md overview
2. Identify issue: Over-serialization at RSC boundary
3. Load minimize-serialization.md
4. Pass only necessary fields, transform on client

Additional Resources

Official Next.js documentation:

• App Router Documentation
• Server Components
• Server Actions
• Authentication Guide
• Performance Optimization