React Guideline: Hooks — Follow rules of hooks. Description: Only call hooks at top level and in React functions. Do: Hooks at component top level. Don't: Hooks in conditions loops or callbacks. Good Example: const [x, setX] = useState(). Bad Example: if (cond) { const [x, setX] = useState() }. Severity: High. Docs: https://react.dev/reference/rules/rules-of-hooks.