React Expert

What it does

When your agent uses it

• Building new React components with TypeScript
• Choosing between Context, Zustand, Redux and TanStack Query for state
• Converting class components to hooks
• Writing forms with React 19 actions and useActionState
• Fixing re-render performance with memoization and lazy loading

Example prompts

• “Build a sortable data table component in TypeScript and test it with React Testing Library.”
• “Convert the legacy UserProfile class component to a function component with hooks.”
• “Move the search state out of prop drilling and into a small Zustand store.”
• “Rewrite the signup form to use useActionState and show server errors inline.”

Requirements

• TypeScript (`tsc`) and React Testing Library

Workflow steps

6 steps, taken from the first numbered list in SKILL.md.

1. 1Analyze requirements - Identify component hierarchy, state needs, data flow
2. 2Choose patterns - Select appropriate state management, data fetching approach
3. 3Implement - Write TypeScript components with proper types
4. 4Validate - Run tsc --noEmit; if it fails, review reported errors, fix all type issues, and re-run until clean before proceeding
5. 5Optimize - Apply memoization where needed, ensure accessibility; if new type errors are introduced, return to step 4
6. 6Test - Write tests with React Testing Library; if any assertions fail, debug and fix before submitting

What it can do on your machine

Read from SKILL.md and the folder at commit 1be15d8. It shows what the files ask for, not the result of running them.

• Tool permissions

  Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

  From allowed-tools in the SKILL.md frontmatter.

• Runs code

  Shell commands in SKILL.md call:

  • tsc

  From the folder's file list and the shell code blocks in SKILL.md.

• Network

  Links to these hosts (documentation or services it may open):

  • github.com
  • synergetic.solutions
  • jeffallan.github.io

  From URLs in SKILL.md, links to its own repository left out.

• Credentials

  Names no API keys, tokens, secrets or passwords.

  From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

React Expert loads about 1.4k tokens when it runs, and up to ~13k if it reads all its reference files. Until then it costs about 100 tokens; SKILL.md has 365 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it

~100

When it runs · the whole SKILL.md, loaded when a task matches

~1.4k

With references · SKILL.md plus every file in references/, read only if the agent opens them

~13k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from Jeffallan/claude-skills at commit 1be15d8, republished under its MIT licence (© Jeffallan). 365 words, ~1,358 tokens.

name

react-expert

description

Use when building React 18+ applications in .jsx or .tsx files, Next.js App Router projects, or create-react-app setups. Creates components, implements custom hooks, debugs rendering issues, migrates class components to functional, and implements state management. Invoke for Server Components, Suspense boundaries, useActionState forms, performance optimization, or React 19 features.

license

MIT

metadata.author

https://github.com/Jeffallan

metadata.company

https://synergetic.solutions

metadata.version

1.1.0

metadata.domain

frontend

metadata.triggers

React, JSX, hooks, useState, useEffect, useContext, Server Components, React 19, Suspense, TanStack Query, Redux, Zustand, component, frontend

metadata.role

specialist

metadata.scope

implementation

metadata.output-format

code

metadata.related-skills

fullstack-guardian, playwright-expert, test-master

// app/users/page.tsx — Server Component, no "use client"
import { db } from '@/lib/db';

interface User {
  id: string;
  name: string;
}

export default async function UsersPage() {
  const users: User[] = await db.user.findMany();

  return (
    <ul>
      {users.map((user) => (
        <li key={user.id}>{user.name}</li>
      ))}
    </ul>
  );
}

'use client';
import { useActionState } from 'react';

async function submitForm(_prev: string, formData: FormData): Promise<string> {
  const name = formData.get('name') as string;
  // perform server action or fetch
  return `Hello, ${name}!`;
}

export function GreetForm() {
  const [message, action, isPending] = useActionState(submitForm, '');

  return (
    <form action={action}>
      <input name="name" required />
      <button type="submit" disabled={isPending}>
        {isPending ? 'Submitting…' : 'Submit'}
      </button>
      {message && <p>{message}</p>}
    </form>
  );
}

import { useState, useEffect } from 'react';

function useWindowWidth(): number {
  const [width, setWidth] = useState(() => window.innerWidth);

  useEffect(() => {
    const handler = () => setWidth(window.innerWidth);
    window.addEventListener('resize', handler);
    return () => window.removeEventListener('resize', handler); // cleanup
  }, []);

  return width;
}

© Jeffallan, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

SKILL.md and 7 other files (references) in skills/react-expert of Jeffallan/claude-skills.

• SKILL.md
• references/hooks-patterns.md
• references/migration-class-to-modern.md
• references/performance.md
• references/react-19-features.md
• references/server-components.md
• references/state-management.md
• references/testing-react.md

Open the folder on GitHubat commit 1be15d8