Developer Tools

The frontend contains a section called Developer Tools.

Screenshot of Home Assistant's Developer Tools.

Section Description
YAML Lets you validate the configuration and trigger a reload or restart
States Sets the representation of an entity
Services Calls services from integrations
Template Renders templates
Events Fires events
Statistics Shows a list of long-term statistic entities
Assist Lets you see how Home Assistant Assist processes a sentence

What can I do with Developer Tools?

The Developer Tools is meant for all (not just for the developers) to quickly try out things - like calling services, updating states, raising events, and publishing messages in MQTT). It is also a necessary tool for those who write custom automations and scripts by hand. The following describes each of the sections in detail.


This section shows all the available entities, their corresponding state and the attribute values. The state and the attribute information is what Home Assistant sees at run time. To update the entity with a new state, or a new attribute value, click on the entity, scroll to the top, and modify the values, and click on “SET STATE” button.

Note that this is the state representation of a device within Home Assistant. That means, it is what Home Assistant sees, and it does not communicate with the actual device in any manner. The updated information can still be used to trigger events, and state changes. To communicate with the actual device, it is recommended to call services in the services section above, instead of updating state.

For example, changing the light.bedroom state from off to on does not turn on the light. If there is an automation that triggers on the state change of the light.bedroom, it will be triggered – even though the actual bulb has not turned on. Also, when the bulb state changes – the state information will be overridden (the refresh icon can be used to retrieve the latest information that Home Assistant has). In other words, the changes that are made through the “States” section are temporary, and is recommended to use for testing purposes only.

The table containing all entities can be filtered for each column. The used search is a wildcard search meaning that if you input “office” in the entity column filter, every entity whose ID matches “*office*” will be shown. You can also add your own wildcards in the search input (e.g., “office*light”). The attribute filter supports separate filters for attribute names and values, separated by a colon “:”. So the filter “location:3” will result in the table showing all entities that have an attribute name that contains “location” and whose attribute value contains “3”.


This section is used to call Services that are available in the ServiceRegistry.

The list of services in the “Service” dropdown are automatically populated based on the integrations that are found in the configuration, automation and script files. If a desired service does not exist, it means either the integration is not configured properly or not defined in the configuration, automation or script files.

When a Service is selected, and if that service requires an entity_id to be passed, the “Entity” dropdown will automatically be populated with corresponding entities.

A Service may also require additional input to be passed. It is commonly referred to as “service data”. The service data is accepted in YAML format, and it may be optional depending on the service.

When an entity is selected from the Entity dropdown, it automatically populates service data with the corresponding entity_id. The service data YAML can then be modified to pass additional [optional] parameters. The following is an illustration on how to call a light.turn_on service.

To turn on a light bulb, use the following steps:

  1. Select light.turn_on from the Service dropdown
  2. Select the entity (typically the light bulb) from the Entity dropdown (if no entity_id is selected, it turns on ALL lights)
  3. If an entity is selected, the service data is populated with basic YAML that will be passed to the service. Additional data can also be passed by updating the YAML as below.
entity_id: light.bedroom
brightness: 255
rgb_color: [255, 0, 0]

Template Editor

The Template Editor provides a way to quickly test templates prior to placing them into automations and scripts. A code editor is on the left side and your real-time output is displayed in the preview on the right side.

By default, this will contain sample code that illustrates how templates can be written and tested. This sample code can be removed and replaced with your own. You can restore the default example by pressing the “Reset to Demo Template” button beneath the code editor.

For more information about Jinja2, visit Jinja2 documentation, and also read templating document here.


In the Events section, you can either fire an event on the event bus or subscribe to an event type in order to view the event data JSON.

Fire an event

To fire an event, simply type the name of the event, and pass the event data in JSON format. For example, to fire a custom event, enter the event_type as event_light_state_changed and the event data JSON as

state: on

If there is an automation that handles that event, it will be automatically triggered. See below:

- alias: "Capture Event"
    platform: event
    event_type: event_light_state_changed
    - service: notify.notify
        message: "Light is turned "

Subscribe to an event

To subscribe to an event, enter the event event type under “Listen to events” and click “Start listening”. Some events types are listed in the Events section under “Active listeners”. You can usually find information about event types for a particular integration in its documentation. You can then examine the event data JSON to find the correct parameters for your automations.

For example, subscribing to the event type of the Shelly integration, returns event data JSON similar to the following on a button press.

Event 0 fired 9:53 AM:
    "event_type": "",
    "data": {
        "device_id": "e09c64a22553484d804353ef97f6fcd6",
        "device": "shellybutton1-A4C12A45174",
        "channel": 1,
        "click_type": "single"
    "origin": "LOCAL",
    "time_fired": "2021-04-28T08:53:12.755729+00:00",
    "context": {
        "id": "e0f379706563aaa0c2c1fda5174b5a0e",
        "parent_id": null,
        "user_id": null


The Statistics tab shows a list of long-term statistic entities. If the long term statistics is not working for an entity, a Fix Issue link is shown. Select it to view a description of the issue. There might also be an option to fix the issue.

Statistics issue message

Another use of the statistics developer tool is to correct any measurements. Select the icon. Use date & time to search for the incorrect data point and adjust the value.

Screenshot showing adjusting the long-term statistic history value


The Assist tab lets you see how Home Assistant’s Assist processes a sentence.

If no matching intent is found, then Assist is unable to interpret the sentence. If a matching intent was found, information is provided on the action that will be performed on which entities. The example below shows how the following sentence was parsed: what lights are on in the office.

  • Assist found a matching intent: HassGetState.
  • It found entities matching the domain: lights.
  • The lights have the state on.
  • The lights are in the area office.
  • The targets are the narrowed-down entities in scope.

Example use of assist developer tools