Private Folders & Colocation

Prefix a folder name with an underscore — _folderName — and Next.js treats it, and everything inside it, as opted out of routing. No file inside a private folder, no matter what it's named, will ever become a route.

Folder structure

Text

app/
  dashboard/
    _components/
      Chart.tsx
      StatCard.tsx
    _lib/
      formatCurrency.ts
    page.tsx          // route: /dashboard
    settings/
      page.tsx        // route: /dashboard/settings

Here, _components/ and _lib/ live right next to the routes that use them, but neither folder — nor anything inside it — is reachable as a URL. Even if someone added a _components/page.tsx by mistake, it would still not become a route.

Why not just colocate directly?

Next.js already lets you place non-route files directly alongside page.tsx in the same folder — this general colocation philosophy is covered on the Project Structure page. Only files with specific reserved names (page.tsx, layout.tsx, loading.tsx, route.ts, and a handful of others) are treated specially by the router; anything else you drop into a route folder is simply ignored by routing and can be imported like any other module.

So why reach for an underscore folder at all? Two situations make it genuinely useful:

Naming collision safety — if you ever wanted a helper file literally named page or layout for non-routing reasons, only a private folder guarantees Next.js will never treat it as a route file.
Visual and structural grouping — bundling a large batch of related helpers, tests, and components under one clearly-labeled _folder keeps a busy route directory readable, rather than scattering many loose files next to page.tsx.
Future-proofing — if Next.js ever reserves a new special filename that happens to match one of your existing colocated files, a private folder is immune to that because the entire folder is excluded from routing, not just specific filenames.

Note

The underscore only needs to prefix the folder itself, not every file inside it. Once a folder is private, every file and nested folder beneath it is automatically excluded from routing too.

Tip

As a rule of thumb: for a single helper file or two, colocate it directly next to page.tsx. Once a route accumulates several supporting files — components, hooks, tests, constants — move them into an underscore-prefixed folder so the route directory stays easy to scan.