Home Assistant uses the YAML syntax for configuration. YAML might take a while to get used to but is really powerful in allowing you to express complex configurations.

For each component that you want to use in Home Assistant, you add code in your configuration.yaml file to specify its settings. The following example entry specifies that you want to use the notify component with the pushbullet platform.

  platform: pushbullet
  api_key: "o.1234abcd"
  name: pushbullet
  • A component provides the core logic for some functionality (like notify provides sending notifications).
  • A platform makes the connection to a specific software or hardware platform (like pushbullet works with the service from pushbullet.com).

The basics of YAML syntax are block collections and mappings containing key-value pairs. Each item in a collection starts with a - while mappings have the format key: value. If you specify duplicate keys, the last value for a key is used.

Note that indentation is an important part of specifying relationships using YAML. Things that are indented are nested “inside” things that are one level higher. So in the above example, platform: pushbullet is a property of (nested inside) the notify component.

Getting the right indentation can be tricky if you’re not using an editor with a fixed width font. Tabs are not allowed to be used for indentation. Convention is to use 2 spaces for each level of indentation.

You can use the online service YAMLLint to check if your YAML syntax is correct before loading it into Home Assistant which will save you some time. If you do so, be aware that this is a thrid-party service and is not maintained by the Home Assistant community.

Please pay attention on not storing private data (passwords, API keys, etc.) directly in your configuration.yaml file. Private data can be stored in a separate file or in environmental variables, which circumvents this problem of security.

Text following a # are comments and are ignored by the system.

The next example shows an input_select component that uses a block collection for the options values. The other properties (like name) are specified using mappings. Note that the second line just has threat: with no value on the same line. Here threat is the name of the input_select and the values for it are everything nested below it.

    name: Threat level
# A collection is used for options
     - 0
     - 1
     - 2
     - 3
    initial: 0

The following example shows nesting a collection of mappings in a mapping. In Home Assistant, this would create two sensors that each use the MQTT platform but have different values for their state_topic (one of the properties used for MQTT sensors).

  - platform: mqtt
    state_topic: sensor/topic
  - platform: mqtt
    state_topic: sensor2/topic

Using Environment Variables

You can include values from your system’s environment variables with !env_var.

  api_password: !env_var PASSWORD

Default Value

If an environment variable is not set, you can fallback to a default value.

  api_password: !env_var PASSWORD default_password

Including Separate Files

To improve readability, you can source out certain domains from you main configuration file with the !include-Syntax.

lights: !include lights.yaml

More information about this feature can also be found at splitting configuration.