---
url: /cli/serve.md
description: >-
  The development server - one process for the whole project, client modules
  through Vite with HMR, API routes hot-reloaded in the same process, on
  devHost.
---

`serve` is the command you leave running while you work.

One process covers every selected folder, and both halves of each:

* client modules go through Vite, with HMR
* API routes run in the same process, hot-reloaded on change
* requests are dispatched between the two by the folder's `backend.base`
* [sidecar](/sidecar/intro.md) entries marked `serve` are watched, rebuilt and restarted

No second command to start, no proxy to configure.

```sh
pnpm dev               # every folder
pnpm dev admin front   # just these two
```

Listens on [kosmo.devHost](/essentials/config.md#project-settings-package-json).

## Dev is always client-rendered

`serve` is Vite + HMR + client-side rendering, whether or not the folder has [SSR enabled](/frontend/server-side-render.md).

Server rendering happens in the production build, so there is no server-rendered markup to look at here.

This catches people out coming from Next, Nuxt or TanStack Start, where dev
mirrors production rendering. To see anything server-rendered, use [kosmo preview](/cli/preview.md).

## Selecting folders

With no arguments, every source folder is served.
Name one or more to narrow the scope - the names are directory names under `src/`.

A name with no `src/<name>/kosmo.config.ts` stops the command before anything runs,
and a project with no folders at all reports `No source folders detected`.

Narrowing changes what the one process serves: folders you left out are not mounted,
so their paths 404 rather than falling through.