- `group`: collections of build targets
- `variable`: build arguments and variables
- `function`: custom Bake functions

You define properties as hierarchical blocks in the Bake file.
You can assign one or more attributes to a property.

The following snippet shows a JSON representation of a simple Bake file.
This Bake file defines three properties: a variable, a group, and a target.

```json
{
  "variable": {
    "TAG": {
      "default": "latest"
    }
  },
  "group": {
    "default": {
      "targets": ["webapp"]
    }
  },
  "target": {
    "webapp": {
      "dockerfile": "Dockerfile",
      "tags": ["docker.io/username/webapp:${TAG}"]
    }
  }
}
```

In the JSON representation of a Bake file, properties are objects,
and attributes are values assigned to those objects.

The following example shows the same Bake file in the HCL format:

```hcl
variable "TAG" {
  default = "latest"
}

group "default" {
  targets = ["webapp"]
}

target "webapp" {
  dockerfile = "Dockerfile"
  tags = ["docker.io/username/webapp:${TAG}"]
}
```

HCL is the preferred format for Bake files.
Aside from syntactic differences,
HCL lets you use features that the JSON and YAML formats don't support.

The examples in this document use the HCL format.

## Target

A target reflects a single `docker build` invocation.
Consider the following build command:

```console
$ docker build \
  --file=Dockerfile.webapp \
  --tag=docker.io/username/webapp:latest \
  https://github.com/username/webapp
```

You can express this command in a Bake file as follows:

```hcl
target "webapp" {
  dockerfile = "Dockerfile.webapp"
  tags = ["docker.io/username/webapp:latest"]
  context = "https://github.com/username/webapp"
}
```

The following table shows the complete list of attributes that you can assign to a target:

| Name                                            | Type    | Description                                                          |
|-------------------------------------------------|---------|----------------------------------------------------------------------|
| [`args`](#targetargs)                           | Map     | Build arguments                                                      |
| [`annotations`](#targetannotations)             | List    | Exporter annotations                                                 |
| [`attest`](#targetattest)                       | List    | Build attestations                                                   |
| [`cache-from`](#targetcache-from)               | List    | External cache sources                                               |
| [`cache-to`](#targetcache-to)                   | List    | External cache destinations                                          |
| [`call`](#targetcall)                           | String  | Specify the frontend method to call for the target.                  |
| [`context`](#targetcontext)                     | String  | Set of files located in the specified path or URL                    |
| [`contexts`](#targetcontexts)                   | Map     | Additional build contexts                                            |
| [`description`](#targetdescription)             | String  | Description of a target                                              |
| [`dockerfile-inline`](#targetdockerfile-inline) | String  | Inline Dockerfile string                                             |
| [`dockerfile`](#targetdockerfile)               | String  | Dockerfile location                                                  |
| [`inherits`](#targetinherits)                   | List    | Inherit attributes from other targets                                |
| [`labels`](#targetlabels)                       | Map     | Metadata for images                                                  |
| [`matrix`](#targetmatrix)                       | Map     | Define a set of variables that forks a target into multiple targets. |
| [`name`](#targetname)                           | String  | Override the target name when using a matrix.                        |