SSR blockers are patterns in your frontend code that prevent server-side rendering from working correctly. AppHandoff's scanner detects common blockers such as direct window or document references outside useEffect hooks, dynamic imports without SSR fallbacks, and localStorage access during initial render.
Each detected blocker appears as a mismatch with a suggested fix. For client-only code, the fix is typically wrapping the access in a useEffect or dynamic import with ssr: false. AppHandoff categorizes blockers by impact level so teams can prioritize fixes that affect critical pages like landing pages and SEO-sensitive routes first.