Bootstrap utilities are generated with our utility API and can be used to modify or extend our default set of utility classes via Sass. Our utility API is based on a series of Sass maps and functions for generating families of classes with various options. If you're unfamiliar with Sass maps, read up on the [official Sass docs](https://sass-lang.com/documentation/values/maps) to get started.
The `$utilities` map contains all our utilities and is later merged with your custom `$utilities` map, if present. The utility map contains a keyed list of utility groups which accept the following options:
| `property` | **Required** | Name of the property, this can be a string or an array of strings (e.g., horizontal paddings or margins). |
| `values` | **Required** | List of values, or a map if you don't want the class name to be the same as the value. If `null` is used as map key, it isn't compiled. |
| `class` | Optional | Variable for the class name if you don't want it to be the same as the property. In case you don't provide the `class` key and `property` key is an array of strings, the class name will be the first element of the `property` array. |
| `responsive` | Optional | Boolean indicating if responsive classes need to be generated. `false` by default. |
| `rfs` | Optional | Boolean to enable fluid rescaling. Have a look at the [RFS]({{< docsref "/getting-started/rfs" >}}) page to find out how this works. `false` by default. |
| `print` | Optional | Boolean indicating if print classes need to be generated. `false` by default. |
All utility variables are added to the `$utilities` variable within our `_utilities.scss` stylesheet. Each group of utilities looks something like this:
New utilities can be added to the default `$utilities` map with a `map-merge`. Make sure our `_utilities.scss` is imported first, then use the `map-merge` to add your additional utilities. For example, here's how to add a responsive `cursor` utility with three values.
Modify existing utilities in the default `$utilities` map with `map-get` and `map-merge` functions. In the example below, we're adding an additional value to the `width` utilities. Start with an initial `map-merge` and then specify which utility you want to modify. From there, fetch the nested `"width"` map with `map-get` to access and modify the utility's options and values.
Remove any of the default utilities by setting the group key to `null`. For example, to remove all our `width` utilities, create a `$utilities``map-merge` and add `"width": null` within.
