YAML syntax

Home Assistant uses the YAML syntax for configuration. While most integrations can be configured through the UI, some integrations require you to edit your configuration.yaml file to specify its settings.

YAML Style Guide

This page gives a high-level introduction to the YAML syntax used in Home Assistant. For a more detailed description and more examples, refer to the YAML Style Guide for Home Assistant developers.

A first example

The following YAML example entry assumes that you would like to set up the notify integration with the pushbullet platform.

notify:
  platform: pushbullet
  api_key: "o.1234abcd"
  name: pushbullet

• An integration 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. This is somewhat similar to a Hash table or more specifically a dictionary in Python. These can be nested as well. Beware that if you specify duplicate keys, the last value for a key is used.

Indentation in YAML

In YAML, indentation is important for specifying relationships. Indented lines are nested inside lines that are one level higher. In the above example, platform: pushbullet is a property of (nested inside) the notify integration.

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. The convention is to use 2 spaces for each level of indentation.

Comments

Strings of text following a # are comments. They are ignored by the system. Comments explain in plain language what a particular code block is supposed to do. For future-you or someone else looking at the file.

Example with comment and nesting

The next example shows an input_select integration that uses a block collection for the values of options. 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. The values for it are everything nested below it.

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

Example of nested mapping

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).

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

Including values

Environment variables

On Home Assistant CoreHome Assistant Core is the heart of Home Assistant itself. It is a Python program that powers every installation type, but can be installed standalone.
[Learn more] installations, you can include values from your system’s environment variables with !env_var. Note that this will only work for Home Assistant CoreHome Assistant Core is the heart of Home Assistant itself. It is a Python program that powers every installation type, but can be installed standalone.
[Learn more] installations, in a scenario where it is possible to specify these. Regular Home Assistant users are recommended to use !include statements instead.

example:
  password: !env_var PASSWORD

Default value

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

example:
  password: !env_var PASSWORD default_password

Including entire files

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

light: !include lights.yaml

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

Common issues

found character ‘\t’

If you see the following message:

found character '\t' that cannot start any token

This means that you’ve mistakenly entered a tab character, instead of spaces.

Upper and lower case

Home Assistant is case sensitive, a state of 'on' is not the same as 'On' or 'ON'. Similarly an entity of group.Doors is not the same as group.doors.

If you’re having trouble, check the case that Home Assistant is reporting in the dev-state menu, under Developer tools.

Booleans

YAML treats Y, true, Yes, ON all as true and n, FALSE, No, off as false. This means that if you want to set the state of an entity to on you must quote it as 'on' otherwise it will be translated as setting the state to true. The same applies to off.

Not quoting the value may generate an error such as:

not a valid value for dictionary value @ data

Validating YAML syntax

With all these indents and rules, it is easy to make a mistake. The best way to check if your YAML syntax is correct (validate) depends on the editor you use. We can’t list them all here.

• If you edit the files directly in Home Assistant, refer to the section: Validating the configuration