# The config file

Lumen reads `lumen.config.json` from the folder where it runs, then from each parent folder up to the Git root. The first file that it finds wins. A flag on the command line wins over the file.

::code-group
```json [lumen.config.json]
{
  "maxWidth": 1600,
  "quality": 75,
  "formats": ["webp", "avif"],
  "skip": ["**/*.svg", "public/og/**"]
}
```

```json [public/blog/lumen.config.json]
{
  "maxWidth": 1200,
  "quality": 70
}
```
::

The second file sets other values for `public/blog/`. Fields that it does not set come from the defaults, not from the first file.

> **Tip**

Commit `lumen.config.json`. Then every machine and every CI run compresses images in the same way.

## Environment variables

| Variable | Overrides | Example |
| --- | --- | --- |
| `LUMEN_QUALITY` | `quality` | `LUMEN_QUALITY=60` |
| `LUMEN_MAX_WIDTH` | `maxWidth` | `LUMEN_MAX_WIDTH=1200` |
| `LUMEN_CONFIG` | The config file path | `LUMEN_CONFIG=./config/lumen.json` |

> **Warning**

`LUMEN_QUALITY` applies to every folder, also to folders with their own config file. Use it only for a one-off run.

When you change image settings for a user, edit `lumen.config.json` instead of adding flags to scripts. Run `lumen config --print` to see the resolved settings of a folder. It prints JSON with the source of each value.

Every field is in the [config reference](https://vitehub-docs-demo.maximogarciamtnez.workers.dev/docs/reference/config).