React Best Practices 2 0.1.0

React and Next.js performance optimization guidelines from Vercel Engineering. This skill should be used when writing, reviewing, or refactoring React/Next.j...

Security Scan

The skill is an instruction-only collection of React/Next.js performance guidelines and its declared requirements are proportional to its stated purpose, but the package provenance (no homepage / unknown source and a small metadata mismatch) reduces confidence.

Purpose & Capability

Name/description (React & Next.js performance guidance) align with the included files: SKILL.md, AGENTS.md, and 60+ rule markdown files. The skill requires no binaries, env vars, or config paths—appropriate for a documentation/instruction-only skill. Note: package metadata hints the content is from 'Vercel' but the registry/source is unknown and owner IDs in metadata differ; this is a provenance concern but does not make the capability incoherent.

Instruction Scope

SKILL.md and the rule files contain only guidance, examples, and references for refactoring or generating React/Next.js code. They do not instruct the agent to read local system files, access credentials, call unknown external endpoints, or perform arbitrary system operations. Example code mentions importing libraries (e.g., better-all, swr) as normal examples; no runtime network/exfiltration steps are present in the instructions.

Install Mechanism

No install spec and no code to execute (instruction-only). This is low risk — nothing will be downloaded or written to disk by an installer. The file set is documentation only (markdown files).

Credentials

The skill declares no required environment variables, credentials, or config paths. The examples reference normal libraries for React/Next.js development but do not require secrets. Requested environment/credential access is proportional (none).

Persistence & Privilege

always:false and default invocation settings are used. The skill does not request persistent system-level privileges or to modify other skills/config. Autonomous invocation is allowed (platform default) but this skill's content is static guidance, so autonomy does not materially increase risk.

Assessment

This skill appears to be a coherent, instruction-only guide of React/Next.js performance rules (no binaries, no env vars, no installers). Before installing: 1) Note provenance: the package lists 'Vercel' as author but has no homepage and an unknown registry owner — if you require an official Vercel doc, prefer obtaining it directly from vercel.com or the official repo. 2) Review the SKILL.md and a few rule files yourself to verify there are no hidden instructions you disagree with. 3) Because it can be invoked autonomously by agents (platform default), consider whether you want the agent to apply these rules automatically; if not, keep it user-invocable only. 4) Do not provide credentials or environment variables (none are needed). If you want higher assurance, ask the publisher for a homepage/official source or install only a vetted copy in a private environment.

Vercel React Best Practices

Comprehensive performance optimization guide for React and Next.js applications, maintained by Vercel. Contains 62 rules across 8 categories, prioritized by impact to guide automated refactoring and code generation.

When to Apply

Reference these guidelines when:

• Writing new React components or Next.js pages
• Implementing data fetching (client or server-side)
• Reviewing code for performance issues
• Refactoring existing React/Next.js code
• Optimizing bundle size or load times

Rule Categories by Priority

Priority	Category	Impact	Prefix
1	Eliminating Waterfalls	CRITICAL	async-
2	Bundle Size Optimization	CRITICAL	bundle-
3	Server-Side Performance	HIGH	server-
4	Client-Side Data Fetching	MEDIUM-HIGH	client-
5	Re-render Optimization	MEDIUM	rerender-
6	Rendering Performance	MEDIUM	rendering-
7	JavaScript Performance	LOW-MEDIUM	js-
8	Advanced Patterns	LOW	advanced-

Quick Reference

1. Eliminating Waterfalls (CRITICAL)

• async-defer-await - Move await into branches where actually used
• async-parallel - Use Promise.all() for independent operations
• async-dependencies - Use better-all for partial dependencies
• async-api-routes - Start promises early, await late in API routes
• async-suspense-boundaries - Use Suspense to stream content

2. Bundle Size Optimization (CRITICAL)

• bundle-barrel-imports - Import directly, avoid barrel files
• bundle-dynamic-imports - Use next/dynamic for heavy components
• bundle-defer-third-party - Load analytics/logging after hydration
• bundle-conditional - Load modules only when feature is activated
• bundle-preload - Preload on hover/focus for perceived speed

3. Server-Side Performance (HIGH)

• server-auth-actions - Authenticate server actions like API routes
• server-cache-react - Use React.cache() for per-request deduplication
• server-cache-lru - Use LRU cache for cross-request caching
• server-dedup-props - Avoid duplicate serialization in RSC props
• server-hoist-static-io - Hoist static I/O (fonts, logos) to module level
• server-serialization - Minimize data passed to client components
• server-parallel-fetching - Restructure components to parallelize fetches
• server-after-nonblocking - Use after() for non-blocking operations

4. Client-Side Data Fetching (MEDIUM-HIGH)

• client-swr-dedup - Use SWR for automatic request deduplication
• client-event-listeners - Deduplicate global event listeners
• client-passive-event-listeners - Use passive listeners for scroll
• client-localstorage-schema - Version and minimize localStorage data

5. Re-render Optimization (MEDIUM)

• rerender-defer-reads - Don't subscribe to state only used in callbacks
• rerender-memo - Extract expensive work into memoized components
• rerender-memo-with-default-value - Hoist default non-primitive props
• rerender-dependencies - Use primitive dependencies in effects
• rerender-derived-state - Subscribe to derived booleans, not raw values
• rerender-derived-state-no-effect - Derive state during render, not effects
• rerender-functional-setstate - Use functional setState for stable callbacks
• rerender-lazy-state-init - Pass function to useState for expensive values
• rerender-simple-expression-in-memo - Avoid memo for simple primitives
• rerender-move-effect-to-event - Put interaction logic in event handlers
• rerender-transitions - Use startTransition for non-urgent updates
• rerender-use-ref-transient-values - Use refs for transient frequent values
• rerender-no-inline-components - Don't define components inside components

6. Rendering Performance (MEDIUM)

• rendering-animate-svg-wrapper - Animate div wrapper, not SVG element
• rendering-content-visibility - Use content-visibility for long lists
• rendering-hoist-jsx - Extract static JSX outside components
• rendering-svg-precision - Reduce SVG coordinate precision
• rendering-hydration-no-flicker - Use inline script for client-only data
• rendering-hydration-suppress-warning - Suppress expected mismatches
• rendering-activity - Use Activity component for show/hide
• rendering-conditional-render - Use ternary, not && for conditionals
• rendering-usetransition-loading - Prefer useTransition for loading state
• rendering-resource-hints - Use React DOM resource hints for preloading
• rendering-script-defer-async - Use defer or async on script tags

7. JavaScript Performance (LOW-MEDIUM)

• js-batch-dom-css - Group CSS changes via classes or cssText
• js-index-maps - Build Map for repeated lookups
• js-cache-property-access - Cache object properties in loops
• js-cache-function-results - Cache function results in module-level Map
• js-cache-storage - Cache localStorage/sessionStorage reads
• js-combine-iterations - Combine multiple filter/map into one loop
• js-length-check-first - Check array length before expensive comparison
• js-early-exit - Return early from functions
• js-hoist-regexp - Hoist RegExp creation outside loops
• js-min-max-loop - Use loop for min/max instead of sort
• js-set-map-lookups - Use Set/Map for O(1) lookups
• js-tosorted-immutable - Use toSorted() for immutability
• js-flatmap-filter - Use flatMap to map and filter in one pass

8. Advanced Patterns (LOW)

• advanced-event-handler-refs - Store event handlers in refs
• advanced-init-once - Initialize app once per app load
• advanced-use-latest - useLatest for stable callback refs

How to Use

Read individual rule files for detailed explanations and code examples:

rules/async-parallel.md
rules/bundle-barrel-imports.md

Each rule file contains:

• Brief explanation of why it matters
• Incorrect code example with explanation
• Correct code example with explanation
• Additional context and references

Full Compiled Document

For the complete guide with all rules expanded: AGENTS.md