What is React Strict Mode and what does it actually do?

Strict Mode is a development only tool that helps find potential problems in your app early, before they cause real bugs. It does not render anything visible itself, but it intentionally runs certain functions twice during development, like component bodies and some effects, to help surface code that accidentally relies on something being run only once.

import { StrictMode } from 'react';

function App() {
  return (
    <StrictMode>
      <MainApp />
    </StrictMode>
  );
}