--- title: "Developer Tools" description: "Description of the Developer Tools." --- The frontend contains a section called "Developer Tools".

Screenshot of Home Assistant's Developer Tools.

| Section |Description | | ------- |----- | | States | Sets the representation of an entity | | Services | Calls services from integrations | | Events | Fires events | | Templates | Renders templates | ## 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. ## States 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". ## Services 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. ```yaml 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](https://jinja.palletsprojects.com/en/latest/templates/), and also read templating document [here](/docs/configuration/templating). ## Events 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 ```yaml state: on ``` If there is an automation that handles that event, it will be automatically triggered. See below: ```yaml - alias: "Capture Event" trigger: platform: event event_type: event_light_state_changed action: - service: notify.notify data: message: "Light is turned {{ trigger.event.data.state }}" ``` ### 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 `shelly.click` of the Shelly integration, returns event data JSON similar to the following on a button press. ```json Event 0 fired 9:53 AM: { "event_type": "shelly.click", "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 } } ```