# Configuration

Aider has many options which can be set with command line switches. Most options can also be set in an `.aider.conf.yml` file which can be placed in your home directory or at the root of your git repo. Or by setting environment variables like `AIDER_xxx` either in your shell or a `.env` file.

Here are 4 equivalent ways of setting an option.

With a command line switch:

```
$ aider --dark-mode
```  
Using a `.aider.conf.yml` file:

```
dark-mode: true
```  
By setting an environment variable:

```
export AIDER_DARK_MODE=true
```  
Using an `.env` file:

```
AIDER_DARK_MODE=true
```

See the [API key configuration docs](/content/docs/config/api-keys.html) for information on how to configure and store your API keys.