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WebSocket API

Home Assistant hosts a WebSocket API at /api/websocket. This API can be used to stream information from a Home Assistant instance to any client that implements WebSockets. We maintain a JavaScript library which we use in our frontend.

Server states

  1. Client connects.
  2. Authentication phase starts.
    • Server sends auth_required message.
    • Client sends auth message.
    • If auth message correct: go to 3.
    • Server sends auth_invalid. Go to 6.
  3. Send auth_ok message
  4. Authentication phase ends.
  5. Command phase starts.
    1. Client can send commands.
    2. Server can send results of previous commands.
  6. Client or server disconnects session.

During the command phase, the client attaches a unique identifier to each message. The server will add this identifier to each message so that the client can link each message to its origin.

Message format

Each API message is a JSON serialized object containing a type key. After the authentication phase messages also must contain an id, an integer that the caller can use to correlate messages to responses.

Example of an auth message:

{
"type": "auth",
"access_token": "ABCDEFGHIJKLMNOPQ"
}
{
"id": 5,
"type":"event",
"event":{
"data":{},
"event_type":"test_event",
"time_fired":"2016-11-26T01:37:24.265429+00:00",
"origin":"LOCAL"
}
}

Authentication phase

When a client connects to the server, the server sends out auth_required.

{
"type": "auth_required",
"ha_version": "2021.5.3"
}

The first message from the client should be an auth message. You can authorize with an access token.

{
"type": "auth",
"access_token": "ABCDEFGH"
}

If the client supplies valid authentication, the authentication phase will complete by the server sending the auth_ok message:

{
"type": "auth_ok",
"ha_version": "2021.5.3"
}

If the data is incorrect, the server will reply with auth_invalid message and disconnect the session.

{
"type": "auth_invalid",
"message": "Invalid password"
}

Command phase

During this phase the client can give commands to the server. The server will respond to each command with a result message indicating when the command is done and if it was successful along with the context of the command.

{
"id": 6,
"type": "result",
"success": true,
"result": {
"context": {
"id": "326ef27d19415c60c492fe330945f954",
"parent_id": null,
"user_id": "31ddb597e03147118cf8d2f8fbea5553"
}
}
}

Subscribe to events

The command subscribe_events will subscribe your client to the event bus. You can either listen to all events or to a specific event type. If you want to listen to multiple event types, you will have to send multiple subscribe_events commands.

{
"id": 18,
"type": "subscribe_events",
// Optional
"event_type": "state_changed"
}

The server will respond with a result message to indicate that the subscription is active.

{
"id": 18,
"type": "result",
"success": true,
"result": null
}

For each event that matches, the server will send a message of type event. The id in the message will point at the original id of the listen_event command.

{
"id": 18,
"type":"event",
"event":{
"data":{
"entity_id":"light.bed_light",
"new_state":{
"entity_id":"light.bed_light",
"last_changed":"2016-11-26T01:37:24.265390+00:00",
"state":"on",
"attributes":{
"rgb_color":[
254,
208,
0
],
"color_temp":380,
"supported_features":147,
"xy_color":[
0.5,
0.5
],
"brightness":180,
"white_value":200,
"friendly_name":"Bed Light"
},
"last_updated":"2016-11-26T01:37:24.265390+00:00",
"context": {
"id": "326ef27d19415c60c492fe330945f954",
"parent_id": null,
"user_id": "31ddb597e03147118cf8d2f8fbea5553"
}
},
"old_state":{
"entity_id":"light.bed_light",
"last_changed":"2016-11-26T01:37:10.466994+00:00",
"state":"off",
"attributes":{
"supported_features":147,
"friendly_name":"Bed Light"
},
"last_updated":"2016-11-26T01:37:10.466994+00:00",
"context": {
"id": "e4af5b117137425e97658041a0538441",
"parent_id": null,
"user_id": "31ddb597e03147118cf8d2f8fbea5553"
}
}
},
"event_type":"state_changed",
"time_fired":"2016-11-26T01:37:24.265429+00:00",
"origin":"LOCAL",
"context": {
"id": "326ef27d19415c60c492fe330945f954",
"parent_id": null,
"user_id": "31ddb597e03147118cf8d2f8fbea5553"
}
}
}

Subscribe to trigger

You can also subscribe to one or more triggers with subscribe_trigger. These are the same triggers syntax as used for automation triggers. You can define one or a list of triggers.

{
"id": 2,
"type": "subscribe_trigger",
"trigger": {
"platform": "state",
"entity_id": "binary_sensor.motion_occupancy",
"from": "off",
"to":"on"
}
}

As a response you get:

{
"id": 2,
"type": "result",
"success": true,
"result": null
}

For each trigger that matches, the server will send a message of type trigger. The id in the message will point at the original id of the subscribe_trigger command. Note that your variables will be different based on the used trigger.

{
"id": 2,
"type": "event",
"event": {
"variables": {
"trigger": {
"id": "0",
"idx": "0",
"platform": "state",
"entity_id": "binary_sensor.motion_occupancy",
"from_state": {
"entity_id": "binary_sensor.motion_occupancy",
"state": "off",
"attributes": {
"device_class": "motion",
"friendly_name": "motion occupancy"
},
"last_changed": "2022-01-09T10:30:37.585143+00:00",
"last_updated": "2022-01-09T10:33:04.388104+00:00",
"context": {
"id": "90e30ad8e6d0c218840478d3c21dd754",
"parent_id": null,
"user_id": null
}
},
"to_state": {
"entity_id": "binary_sensor.motion_occupancy",
"state": "on",
"attributes": {
"device_class": "motion",
"friendly_name": "motion occupancy"
},
"last_changed": "2022-01-09T10:33:04.391956+00:00",
"last_updated": "2022-01-09T10:33:04.391956+00:00",
"context": {
"id": "9b263f9e4e899819a0515a97f6ddfb47",
"parent_id": null,
"user_id": null
}
},
"for": null,
"attribute": null,
"description": "state of binary_sensor.motion_occupancy"
}
},
"context": {
"id": "9b263f9e4e899819a0515a97f6ddfb47",
"parent_id": null,
"user_id": null
}
}
}

Unsubscribing from events

You can unsubscribe from previously created subscriptions. Pass the id of the original subscription command as value to the subscription field.

{
"id": 19,
"type": "unsubscribe_events",
"subscription": 18
}

The server will respond with a result message to indicate that unsubscribing was successful.

{
"id": 19,
"type": "result",
"success": true,
"result": null
}

Fire an event

This will fire an event on the Home Assistant event bus.

{
"id": 24,
"type": "fire_event",
"event_type": "mydomain_event",
// Optional
"event_data": {
"device_id": "my-device-id",
"type": "motion_detected"
}
}

The server will respond with a result message to indicate that the event was fired successful.

{
"id": 24,
"type": "result",
"success": true,
"result": {
"context": {
"id": "326ef27d19415c60c492fe330945f954",
"parent_id": null,
"user_id": "31ddb597e03147118cf8d2f8fbea5553"
}
}
}

Calling a service

This will call a service in Home Assistant. Right now there is no return value. The client can listen to state_changed events if it is interested in changed entities as a result of a service call.

{
"id": 24,
"type": "call_service",
"domain": "light",
"service": "turn_on",
// Optional
"service_data": {
"color_name": "beige",
"brightness": "101"
}
// Optional
"target": {
"entity_id": "light.kitchen"
}
// Must be included for services that return response data
"return_response": true
}

The server will indicate with a message indicating that the service is done executing.

{
"id": 24,
"type": "result",
"success": true,
"result": {
"context": {
"id": "326ef27d19415c60c492fe330945f954",
"parent_id": null,
"user_id": "31ddb597e03147118cf8d2f8fbea5553"
},
"response": null
}
}

The result of the call will always include a response to account for services that support responses. When a service that doesn't support responses is called, the value of response will be null.

Fetching states

This will get a dump of all the current states in Home Assistant.

{
"id": 19,
"type": "get_states"
}

The server will respond with a result message containing the states.

{
"id": 19,
"type": "result",
"success": true,
"result": [ ... ]
}

Fetching config

This will get a dump of the current config in Home Assistant.

{
"id": 19,
"type": "get_config"
}

The server will respond with a result message containing the config.

{
"id": 19,
"type": "result",
"success": true,
"result": { ... }
}

Fetching services

This will get a dump of the current services in Home Assistant.

{
"id": 19,
"type": "get_services"
}

The server will respond with a result message containing the services.

{
"id": 19,
"type": "result",
"success": true,
"result": { ... }
}

Fetching panels

This will get a dump of the current registered panels in Home Assistant.

{
"id": 19,
"type": "get_panels"
}

The server will respond with a result message containing the current registered panels.

{
"id": 19,
"type": "result",
"success": true,
"result": [ ... ]
}

Pings and pongs

The API supports receiving a ping from the client and returning a pong. This serves as a heartbeat to ensure the connection is still alive:

{
"id": 19,
"type": "ping"
}

The server must send a pong back as quickly as possible, if the connection is still active:

{
"id": 19,
"type": "pong"
}

Validate config

This command allows you to validate triggers, conditions and action configurations. The keys trigger, condition and action will be validated as if part of an automation (so a list of triggers/conditions/actions is also allowed). All fields are optional and the result will only contain keys that were passed in.

{
"id": 19,
"type": "validate_config",
"trigger": ...,
"condition": ...,
"action": ...
}

The server will respond with the validation results. Only fields will be included in the response that were also included in the command message.

{
"id": 19,
"type": "result",
"success": true,
"result": {
"trigger": {"valid": true, "error": null},
"condition": {"valid": false, "error": "Invalid condition specified for data[0]"},
"action": {"valid": true, "error": null}
}
}

Error handling

If an error occurs, the success key in the result message will be set to false. It will contain an error key containing an object with two keys: code and message.

{
"id": 12,
"type":"result",
"success": false,
"error": {
"code": "invalid_format",
"message": "Message incorrectly formatted: expected str for dictionary value @ data['event_type']. Got 100"
}
}

Error handling during service calls and translations

The JSON below shows an example of an error response. If HomeAssistantError error (or a subclass of HomeAssistantError) is handled, translation information, if set, will be added to the response.

When handling ServiceValidationError (service_validation_error) a stack trace is printed to the logs at debug level only.

{
"id": 24,
"type":"result",
"success": false,
"error": {
"code": "service_validation_error",
"message": "Option 'custom' is not a supported mode.",
"translation_key": "unsupported_mode",
"translation_domain": "kitchen_sink",
"translation_placeholders": {
"mode": "custom"
}
}
}

Read more about raising exceptions or and the localization of exceptions.