App Router file conventions

The file system is the router

In the App Router, a folder inside app/ is a URL segment and a page file inside that folder makes the segment routable. A folder without a page file still shapes the URL — it just has nothing to render on its own.

A handful of reserved filenames carry meaning, and everything else in the folder is ordinary code you can colocate next to the route that uses it.

• page: the UI for this route, and the only file that makes a segment publicly reachable
• layout: shared chrome that wraps this segment and everything nested below it
• loading: the fallback shown while this segment streams in
• error: the boundary that catches a render error in this segment
• not-found: what renders when the segment calls notFound()

Because the conventions are filenames rather than configuration, a route is always discoverable by reading the directory tree — there is no central routes file to drift out of date.