`next build` creates an optimized production build of your application. The output displays information about each route.
- **Size** – The number of assets downloaded when navigating to the page client-side. The size for each route only includes its dependencies.
- **First Load JS** – The number of assets downloaded when visiting the page from the server. The amount of JS shared by all is shown as a separate metric.
You can enable production profiling for React with the `--profile` flag in `next build`. This requires [Next.js 9.5](https://nextjs.org/blog/next-9-5):
> Note: `PORT` can not be set in `.env` as booting up the HTTP server happens before any other code is initialized.
You can also set the hostname to be different from the default of `0.0.0.0`, this can be useful for making the application available for other devices on the network. The default hostname can be changed with `-H`, like so:
`next info` prints relevant details about the current system which can be used to report Next.js bugs.
This information includes Operating System platform/arch/version, Binaries (Node.js, npm, Yarn, pnpm) and npm package versions (`next`, `react`, `react-dom`).
Running the following in your project's root directory:
```bash
next info
```
will give you information like this example:
```bash
Operating System:
Platform: linux
Arch: x64
Version: #22-Ubuntu SMP Fri Nov 5 13:21:36 UTC 2021
Binaries:
Node: 16.13.0
npm: 8.1.0
Yarn: 1.22.17
pnpm: 6.24.2
Relevant packages:
next: 12.0.8
react: 17.0.2
react-dom: 17.0.2
```
This information should then be pasted into GitHub Issues.