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What are React Developer Tools and how do you use them?

Q: What are React Developer Tools and how do you use them?

**Core concept (TL;DR).** React DevTools is a **browser extension** (and standalone app) that adds two panels: **Components** — inspect the component tree with each node's props, state, and hooks (editable live) — and **Profiler** — record renders to see **which** components rendered, **why**, and **how long** they took. Two panels: inspect tree · profile renders Components <text x="135" y="86" fill=

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A component whose state you'd inspect in DevTools

import { useState } from "react";

// In the Components panel you'd see App's hooks: [count, theme].
// In the Profiler you'd see only the text node update each click.
export default function App() {
  const [count, setCount] = useState(0);
  const [theme] = useState("dark");
  return (
    <div style={{ padding: 24, fontFamily: "system-ui" }}>
      <p>count={count} theme={theme}</p>
      <button onClick={() => setCount((c) => c + 1)}>+1</button>
    </div>
  );
}

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