Control Home Assistant devices and automate via the REST API and WebSocket API

Steps

1. Generate a Long-Lived Access Token in the Home Assistant user profile page; all API calls require the header Authorization: Bearer <TOKEN>
2. Test connectivity with GET http://<ha-host>:8123/api/ which returns {"message":"API running"} if the HTTP integration is enabled and the token is valid
3. Control entities via POST http://<ha-host>:8123/api/services/<domain>/<service> with a JSON body such as {"entity_id":"light.living_room"}; for example POST /api/services/light/turn_on with {"entity_id":"light.x","brightness":200}
4. Subscribe to state changes in real time using the WebSocket API: connect to ws://<ha-host>:8123/api/websocket, respond to the auth_required message with {"type":"auth","access_token":"<TOKEN>"}, then send a subscribe_events command
5. Retrieve the current state of an entity with GET /api/states/<entity_id>; retrieve all states with GET /api/states; use the state object's attributes map for entity-specific properties (color, brightness, temperature, etc.)
6. Trigger automations or scripts directly via the services API: POST /api/services/automation/trigger with {"entity_id":"automation.<name>"} or POST /api/services/script/turn_on