Device detection that's right in CSR and SSR

import { useDevice } from 'react-device-check';

export default function Page() {
  const { type, os, isMobile, isHydrated } = useDevice();

  // Server render & hydration first paint: type = 'desktop', isHydrated = false.
  // One render later the real device shows up. No mismatch, ever.
  if (!isHydrated) return <Skeleton />;

  if (isMobile && os === 'ios') return <AppStoreBanner />;
  return <p>You are on a {type} running {os}.</p>;
}

import { useIsMobile, useOS } from 'react-device-check';

export default function DownloadButton() {
  const isMobile = useIsMobile(); // boolean only, ~1.1 kB total
  const os = useOS(); // 'ios' | 'android' | ...

  if (isMobile && os === 'ios') return <AppStoreButton />;
  if (isMobile && os === 'android') return <PlayStoreButton />;
  return <DesktopDownloadButton />;
}

import { detectDevice } from 'react-device-check';

export function middleware(request: Request) {
  // No React, no globals. Inject the signals you have
  const { type } = detectDevice({
    ua: request.headers.get('user-agent') ?? '',
  });

  if (type === 'mobile') {
    // e.g. rewrite to the lightweight variant
  }
}