Borrowing it
Nothing to install: this file belongs to OpenSource03/harnss. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/OpenSource03/harnss/master/.agents/skills/vercel-react-best-practices/SKILL.mdgit clone --depth 1 https://github.com/OpenSource03/harnssWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/opensource03/harnss/vercel-react-best-practices)<a href="https://agentmods.dev/skills/opensource03/harnss/vercel-react-best-practices"><img src="https://agentmods.dev/badge/skills/opensource03/harnss/vercel-react-best-practices/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/opensource03/harnss/vercel-react-best-practices"><img src="https://agentmods.dev/badge/skills/opensource03/harnss/vercel-react-best-practices.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00067 | $0.01594 |
| Opus 5.5 | $0.00027 | $0.00638 |
| Sonnet 5.5 | $0.00013 | $0.00319 |
| Haiku 4.5 | $0.00007 | $0.00159 |
Grade A, and why
vercel-react-best-practices scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 1mo ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
This is a copy
86% identical to react-performance — 13 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.
How it starts
The opening of the file, as written. The whole thing — 142 lines — stays where its author put it; the contents beside it link to each section on GitHub.
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 usedasync-parallel- Use Promise.all() for independent operationsasync-dependencies- Use better-all for partial dependenciesasync-api-routes- Start promises early, await late in API routesasync-suspense-boundaries- Use Suspense to stream content
2. Bundle Size Optimization (CRITICAL)
bundle-barrel-imports- Import directly, avoid barrel filesbundle-dynamic-imports- Use next/dynamic for heavy componentsbundle-defer-third-party- Load analytics/logging after hydrationbundle-conditional- Load modules only when feature is activatedbundle-preload- Preload on hover/focus for perceived speed
3. Server-Side Performance (HIGH)
server-auth-actions- Authenticate server actions like API routesserver-cache-react- Use React.cache() for per-request deduplicationserver-cache-lru- Use LRU cache for cross-request cachingserver-dedup-props- Avoid duplicate serialization in RSC propsserver-hoist-static-io- Hoist static I/O (fonts, logos) to module levelserver-serialization- Minimize data passed to client componentsserver-parallel-fetching- Restructure components to parallelize fetchesserver-after-nonblocking- Use after() for non-blocking operations
What ships with it
60 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
- AGENTS.md 89 KB
- README.md 3.3 KB
- rules/_sections.md 1.5 KB
- rules/_template.md 631 B
- rules/advanced-event-handler-refs.md 1.4 KB
- rules/advanced-init-once.md 958 B
- rules/advanced-use-latest.md 1.0 KB
- rules/async-api-routes.md 1.1 KB
- rules/async-defer-await.md 2.0 KB
- rules/async-dependencies.md 1.3 KB
- rules/async-parallel.md 654 B
- rules/async-suspense-boundaries.md 2.5 KB
- rules/bundle-barrel-imports.md 2.3 KB
- rules/bundle-conditional.md 949 B
- rules/bundle-defer-third-party.md 920 B
- rules/bundle-dynamic-imports.md 791 B
- rules/bundle-preload.md 1.1 KB
- rules/client-event-listeners.md 1.9 KB
- rules/client-localstorage-schema.md 1.9 KB
- rules/client-passive-event-listeners.md 1.6 KB
- rules/client-swr-dedup.md 1.1 KB
- rules/js-batch-dom-css.md 3.2 KB
- rules/js-cache-function-results.md 1.9 KB
- rules/js-cache-property-access.md 532 B
- rules/js-cache-storage.md 1.6 KB
- rules/js-combine-iterations.md 753 B
- rules/js-early-exit.md 1.1 KB
- rules/js-flatmap-filter.md 1.4 KB
- rules/js-hoist-regexp.md 1.0 KB
- rules/js-index-maps.md 837 B
- rules/js-length-check-first.md 1.7 KB
- rules/js-min-max-loop.md 2.2 KB
- rules/js-set-map-lookups.md 532 B
- rules/js-tosorted-immutable.md 1.7 KB
- rules/rendering-activity.md 564 B
- rules/rendering-animate-svg-wrapper.md 1.2 KB
- rules/rendering-conditional-render.md 980 B
- rules/rendering-content-visibility.md 815 B
- rules/rendering-hoist-jsx.md 1.0 KB
- rules/rendering-hydration-no-flicker.md 2.3 KB
- rules/rendering-hydration-suppress-warning.md 872 B
- rules/rendering-resource-hints.md 2.5 KB
- rules/rendering-script-defer-async.md 1.8 KB
- rules/rendering-svg-precision.md 588 B
- rules/rendering-usetransition-loading.md 2.0 KB
- rules/rerender-defer-reads.md 973 B
- rules/rerender-dependencies.md 824 B
- rules/rerender-derived-state-no-effect.md 1.2 KB
- rules/rerender-derived-state.md 728 B
- rules/rerender-functional-setstate.md 2.9 KB
- rules/rerender-lazy-state-init.md 2.0 KB
- rules/rerender-memo-with-default-value.md 1.1 KB
- rules/rerender-memo.md 1.1 KB
- rules/rerender-move-effect-to-event.md 1.2 KB
- rules/rerender-no-inline-components.md 2.1 KB
- rules/rerender-simple-expression-in-memo.md 1018 B
- rules/rerender-transitions.md 1.0 KB
- rules/rerender-use-ref-transient-values.md 1.7 KB
- rules/server-after-nonblocking.md 2.0 KB
- rules/server-auth-actions.md 2.6 KB
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 1mo ago First seen · 142 lines · 67 tokens per session scan A 0ae7b4706da6
vercel-react-best-practices is a skill published in the GitHub repository OpenSource03/harnss (392 stars, last pushed 7d ago), licensed MIT. It adds 67 tokens to every session and 1,594 once invoked, about $0.0003 per session on Opus 5.5. A static security scan graded it A with 0 findings. It is 86% identical to react-performance, differing in 13 lines, and is treated as a copy.
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