getServerSideProps vs getStaticProps — what's the difference?

These are Pages Router APIs, i.e. the pages/ directory.

getServerSideProps fetches data on the server for every request to the page. getStaticProps is for static generation — usually at build time, and with ISR also during regeneration.

// pages/profile.jsx — outline
export async function getServerSideProps() {
  return { props: { generatedAt: new Date().toISOString() } };
}

export default function Profile({ generatedAt }) {
  return <p>{generatedAt}</p>;
}

Pitfall: I don't carry these functions over to app/. The App Router uses a different data-fetching and caching model. Props are sent to the client — I don't put secrets in them.