Borrowing it
Nothing to install: this file belongs to extra-org/extra. 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/extra-org/extra/main/.claude/skills/vercel-react-best-practices/SKILL.mdgit clone --depth 1 https://github.com/extra-org/extraWrote 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/extra-org/extra/vercel-react-best-practices)<a href="https://agentmods.dev/skills/extra-org/extra/vercel-react-best-practices"><img src="https://agentmods.dev/badge/skills/extra-org/extra/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/extra-org/extra/vercel-react-best-practices"><img src="https://agentmods.dev/badge/skills/extra-org/extra/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 | $0.00039 | $0.01357 |
| Opus 5.5 | $0.00016 | $0.00543 |
| Sonnet 5.5 | $0.00008 | $0.00271 |
| Haiku 4.5 | $0.00004 | $0.00136 |
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 11d 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.
How it starts
The opening of the file, as written. The whole thing — 119 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Skill: Vercel React Best Practices
Purpose
Apply Vercel's performance guidance to Extra's React chat widget. The 70
upstream rules and examples are available locally under
.ai/references/vercel-react-best-practices/rules/; read the rules relevant
to the change rather than loading the entire collection.
All paths in this playbook are relative to the repository root, including when reading a generated Codex or Claude adapter.
When to Use This Skill
- Implementing or reviewing components under
src/agent_manager/api/static/widget/react/. - Changing widget effects, event listeners, state, or data fetching.
- Investigating slow rendering, unnecessary requests, or bundle growth.
Files to Read First
AGENTS.mdand.ai/skills/project-architecture.md.docs/WIDGET_ARCHITECTURE.mdanddocs/WIDGET.md.package.json, the components being changed, and their existing tests.- Relevant rules from the local reference directory, using this routing table:
| Concern | Rule prefix | Starting point |
|---|---|---|
| Sequential independent requests | async- |
async-parallel.md |
| Unnecessary module loading | bundle- |
bundle-conditional.md |
| Duplicate browser subscriptions | client- |
client-event-listeners.md |
| Stale state or unnecessary renders | rerender- |
rerender-functional-setstate.md, rerender-dependencies.md |
| Expensive rendering | rendering- |
rendering-hoist-jsx.md, rendering-content-visibility.md |
| Repeated JavaScript work | js- |
js-set-map-lookups.md, js-combine-iterations.md |
| Callback and initialization patterns | advanced- |
advanced-event-handler-refs.md |
| Server rendering, if introduced separately | server- |
server-no-shared-module-state.md |
Core Principles
- The shipped widget is React inside a custom element and Shadow DOM, bundled
with esbuild. Select rules that fit that environment; Next.js routing, RSC,
SSR caching, and
next/dynamicexamples do not justify adding Next.js. - Prioritize observable request waterfalls, bundle growth, and rendering costs
over speculative micro-optimizations. Match APIs to the installed React
version and esbuild browser target in
package.json. - Preserve custom-element attributes/events, Shadow DOM styling, stream ownership, cancellation, and approval behavior while optimizing components.
- Keep request-specific identity and credentials out of shared caches.
- Treat upstream examples as guidance. Add dependencies or abstractions only when the concrete change benefits from them.
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.
- 11d ago First seen · 119 lines · 39 tokens per session scan A 44b067f78605
vercel-react-best-practices is a skill published in the GitHub repository extra-org/extra (117 stars, last pushed 5d ago), licensed MIT. It adds 39 tokens to every session and 1,357 once invoked, about $0.0002 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-10-19.
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