URLs are clean and human-readable

Hash-based routing (/#/about) is invisible to every search crawler: the entire site is treated as a single URL because servers do not receive anything after the #. Query-string routing (/?page=about) is indexable but ambiguous — Google often merges parameterized URLs into one canonical, splits PageRank across permutations, and rate-limits crawling. Clean path-based URLs are also more shareable, more memorable, and easier to parse in analytics reports.

Move to the framework's file-system router. In Next.js App Router, each folder under app/ with a page.tsx becomes a path segment — no config required. Delete client-side-only hash routers like HashRouter from react-router-dom and replace with BrowserRouter (for a standalone SPA) or the framework-native router.

app/
  page.tsx               -> /
  about/page.tsx         -> /about
  blog/[slug]/page.tsx   -> /blog/my-post

Add permanent redirects in next.config.js from the old hash URLs to the new paths to preserve any existing backlinks.