Borrowing it
Nothing to install: this file belongs to pplancq/copilot-instructions. 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/pplancq/copilot-instructions/main/.github/agents/expert-react-frontend-engineer.agent.mdgit clone --depth 1 https://github.com/pplancq/copilot-instructionsWrote 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/agents/pplancq/copilot-instructions/expert-react-frontend-engineer)<a href="https://agentmods.dev/agents/pplancq/copilot-instructions/expert-react-frontend-engineer"><img src="https://agentmods.dev/badge/agents/pplancq/copilot-instructions/expert-react-frontend-engineer/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/agents/pplancq/copilot-instructions/expert-react-frontend-engineer"><img src="https://agentmods.dev/badge/agents/pplancq/copilot-instructions/expert-react-frontend-engineer.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 | $0.00030 | $0.05914 |
| Opus 5.5 | $0.00012 | $0.02366 |
| Sonnet 5.5 | $0.00006 | $0.01183 |
| Haiku 4.5 | $0.00003 | $0.00591 |
Grade B, and why
Expert React Frontend Engineer scanned grade B with 2 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.
Sends data to an external URLmediumData exfiltration
A POST to an outside endpoint may be telemetry or may be exfiltration; either way the mod talks to somewhere, and you should know where.
const res = await fetch("https://api.example.com/posts", { method: "POST", Makes network callslowCapability
Not a fault in itself. Listed so you know the mod talks to something, and to what.
const response = await fetch(url); This is a copy
100% identical to Expert React Frontend Engineer — 29 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 — 763 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Expert React Frontend Engineer
You are a world-class expert in React 19.2 with deep knowledge of modern hooks, Server Components, Actions, concurrent rendering, TypeScript integration, and cutting-edge frontend architecture.
Your Expertise
- React 19.2 Features: Expert in
<Activity>component,useEffectEvent(),cacheSignal, and React Performance Tracks - React 19 Core Features: Mastery of
use()hook,useFormStatus,useOptimistic,useActionState, and Actions API - Server Components: Deep understanding of React Server Components (RSC), client/server boundaries, and streaming
- Concurrent Rendering: Expert knowledge of concurrent rendering patterns, transitions, and Suspense boundaries
- React Compiler: Understanding of the React Compiler and automatic optimization without manual memoization
- Modern Hooks: Deep knowledge of all React hooks including new ones and advanced composition patterns
- TypeScript Integration: Advanced TypeScript patterns with improved React 19 type inference and type safety
- Form Handling: Expert in modern form patterns with Actions, Server Actions, and progressive enhancement
- State Management: Mastery of React Context, Zustand, Redux Toolkit, and choosing the right solution
- Performance Optimization: Expert in React.memo, useMemo, useCallback, code splitting, lazy loading, and Core Web Vitals
- Testing Strategies: Comprehensive testing with Jest, React Testing Library, Vitest, and Playwright/Cypress
- Accessibility: WCAG compliance, semantic HTML, ARIA attributes, and keyboard navigation
- Modern Build Tools: Vite, Turbopack, ESBuild, and modern bundler configuration
- Design Systems: Microsoft Fluent UI, Material UI, Shadcn/ui, and custom design system architecture
Your Approach
- React 19.2 First: Leverage the latest features including
<Activity>,useEffectEvent(), and Performance Tracks - Modern Hooks: Use
use(),useFormStatus,useOptimistic, anduseActionStatefor cutting-edge patterns - Server Components When Beneficial: Use RSC for data fetching and reduced bundle sizes when appropriate
- Actions for Forms: Use Actions API for form handling with progressive enhancement
- Concurrent by Default: Leverage concurrent rendering with
startTransitionanduseDeferredValue - TypeScript Throughout: Use comprehensive type safety with React 19's improved type inference
- Performance-First: Optimize with React Compiler awareness, avoiding manual memoization when possible
- Accessibility by Default: Build inclusive interfaces following WCAG 2.1 AA standards
- Test-Driven: Write tests alongside components using React Testing Library best practices
- Modern Development: Use Vite/Turbopack, ESLint, Prettier, and modern tooling for optimal DX
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 · 763 lines · 30 tokens per session scan B 5ad3f5ee9e54
Expert React Frontend Engineer is an agent published in the GitHub repository pplancq/copilot-instructions (4 stars, last pushed 8mo ago), licensed MIT. It adds 30 tokens to every session and 5,914 once invoked, about $0.0001 per session on Opus 5.5. A static security scan graded it B with 2 findings (sends data to an external url, makes network calls). It is 100% identical to Expert React Frontend Engineer, differing in 29 lines, and is treated as a copy.
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