Do you need to...
│
├─ GET INFORMATION?
│  ├─ Get one entity's state?        → GET /api/states/{entity_id}
│  ├─ Get all entity states?         → GET /api/states (then filter)
│  ├─ Get configuration?             → GET /api/config
│  ├─ List available services?       → GET /api/services
│  ├─ Discover event types?          → GET /api/events
│  ├─ Query historical data?         → GET /api/history/period/{timestamp}
│  ├─ Get error log?                 → GET /api/error_log
│  ├─ Complex query/computation?     → POST /api/template
│  └─ Check system status?           → GET /api/
│
├─ CONTROL A DEVICE?
│  ├─ Light (on/off/brightness)?     → POST /api/services/light/{service}
│  ├─ Switch?                        → POST /api/services/switch/{service}
│  ├─ Climate/thermostat?            → POST /api/services/climate/{service}
│  ├─ Lock?                          → POST /api/services/lock/{service}
│  ├─ Cover/blinds?                  → POST /api/services/cover/{service}
│  ├─ Media player?                  → POST /api/services/media_player/{service}
│  ├─ Fan?                           → POST /api/services/fan/{service}
│  ├─ Camera?                        → POST /api/services/camera/{service}
│  └─ Any service?                   → POST /api/services/{domain}/{service}
│
├─ MODIFY STATE (NOT FOR DEVICE CONTROL)?
│  ├─ Create/update state?           → POST /api/states/{entity_id}
│  ├─ Delete state?                  → DELETE /api/states/{entity_id}
│  └─ Fire custom event?             → POST /api/events/{event_type}
│
└─ MANAGE SYSTEM?
   ├─ Validate config?               → POST /api/config/core/check_config
   ├─ Reload config?                 → POST /api/services/homeassistant/reload_core_config
   ├─ Restart Home Assistant?        → POST /api/services/homeassistant/restart
   ├─ Get components list?           → GET /api/components
   ├─ Update entity metadata?        → POST /api/services/homeassistant/update_entity
   └─ Check error log?               → GET /api/error_log

# Get one light's state
GET /api/states/light.kitchen

# Get temperature reading
GET /api/states/sensor.temperature

# Get all lights
GET /api/states
# Then filter: .[] | select(.entity_id | startswith("light."))

# Turn on light with brightness
POST /api/services/light/turn_on
{"entity_id": "light.kitchen", "brightness": 200}

# Turn off all lights
POST /api/services/light/turn_off
{"entity_id": "all"}

# Toggle switch
POST /api/services/switch/toggle
{"entity_id": "switch.coffee_maker"}

GET /api/states/light.kitchen
GET /api/states/light.living_room
GET /api/states/light.bedroom

GET /api/states
# Filter in client: select by entity_id prefix

POST /api/template
{"template": "{{ states.light | selectattr('state', 'eq', 'on') | list | length }}"}

# Bad: Multiple sequential API calls
POST /api/services/light/turn_on {"entity_id": "light.kitchen"}
POST /api/services/light/turn_on {"entity_id": "light.living_room"}
POST /api/services/light/turn_on {"entity_id": "light.bedroom"}

# Better: Array of entities in one call
POST /api/services/light/turn_on
{"entity_id": ["light.kitchen", "light.living_room", "light.bedroom"]}

# Best: Use Home Assistant script (for complex multi-step)
POST /api/services/script/turn_on
{"entity_id": "script.my_scene"}

{
  "entity_id": "light.kitchen",
  "state": "on",
  "attributes": {...},
  "last_changed": "...",
  "last_updated": "...",
  "context": {...}
}

{
  "error": "Unauthorized",
  "message": "Invalid authentication provided"
}

{
  "error": "Entity not found",
  "message": "No entity found for domain 'light' and name 'nonexistent'"
}

{
  "error": "Invalid JSON",
  "message": "..."
}

import requests

class HomeAssistant:
    def __init__(self, url, token):
        self.url = url
        self.headers = {
            "Authorization": f"Bearer {token}",
            "Content-Type": "application/json"
        }
    
    # State queries
    def get_state(self, entity_id):
        """Load: state-management.md"""
        return requests.get(f"{self.url}/api/states/{entity_id}", 
                          headers=self.headers).json()
    
    # Service calls
    def turn_on_light(self, entity_id, brightness=None):
        """Load: service-reference.md + entity-types.md"""
        data = {"entity_id": entity_id}
        if brightness:
            data["brightness"] = brightness
        
        return requests.post(
            f"{self.url}/api/services/light/turn_on",
            headers=self.headers,
            json=data
        ).json()
    
    # Complex queries
    def count_on_lights(self):
        """Load: templates.md"""
        template = "{{ states.light | selectattr('state', 'eq', 'on') | list | length }}"
        resp = requests.post(
            f"{self.url}/api/template",
            headers=self.headers,
            json={"template": template}
        )
        return int(resp.json()['result'])

# Usage
ha = HomeAssistant("http://localhost:8123", "YOUR_TOKEN")

# Query state
kitchen = ha.get_state("light.kitchen")
print(f"Kitchen light: {kitchen['state']}")

# Control device
ha.turn_on_light("light.kitchen", brightness=200)

# Complex query
count = ha.count_on_lights()
print(f"{count} lights are on")