Home Assistant API Integration

Master Home Assistant's REST and WebSocket APIs for external integration, state management, and real-time communication.

⚠️ BEFORE YOU START

This skill prevents 5 common API integration errors and saves ~30% token overhead.

Known Issues This Skill Prevents

1. Incorrect authentication headers - Bearer tokens must be prefixed with "Bearer " in Authorization header
2. WebSocket lifecycle management - Missing auth_required handling or improper state subscription
3. State format mismatches - Confusing state vs. attributes; incorrect JSON payload structure
4. Error response handling - Not distinguishing between 4xx client errors and 5xx server errors
5. Service call domain/service mismatch - Incorrect routing to service endpoints

Quick Start

Step 1: Authentication Setup

# In Home Assistant UI:
# Settings → My Home → Create Long-Lived Access Token
# Store token securely (never commit to git)

export HA_TOKEN="eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9..."
export HA_URL="http://192.168.1.100:8123"

Why this matters: All API requests require Bearer token authentication. Creating a dedicated token for external apps allows you to revoke access without changing your password.

Step 2: Test REST API Connectivity

# Get all entity states
curl -X GET "${HA_URL}/api/states" \
  -H "Authorization: Bearer ${HA_TOKEN}" \
  -H "Content-Type: application/json"

Why this matters: Verifies your Home Assistant instance is accessible and your token is valid before building complex integrations.

Step 3: Choose API Type

• REST API: For one-time requests, state queries, service calls (HTTP polling)
• WebSocket API: For real-time events, continuous subscriptions, lower latency (~50ms vs. seconds)

Why this matters: Different use cases require different APIs. WebSocket excels at real-time apps; REST is simpler for occasional requests.

Critical Rules

✅ Always Do

• ✅ Store access tokens in environment variables or secure vaults (never hardcode)
• ✅ Include "Bearer " prefix in Authorization header (exact case and spacing required)
• ✅ Validate WebSocket auth_required messages before sending other commands
• ✅ Handle HTTP errors (401 = token invalid/expired, 404 = entity not found, 502 = HA unavailable)
• ✅ Specify full domain/service for service calls (e.g., "light/turn_on" not just "turn_on")

❌ Never Do

• ❌ Commit access tokens to git or share in logs
• ❌ Skip the initial WebSocket auth handshake
• ❌ Mix Bearer token authentication with username/password
• ❌ Assume state values are always strings (can be "on", 123, or null)
• ❌ Call service endpoints with entity_id as path parameter (use JSON payload instead)

Common Mistakes

❌ Wrong - Missing Bearer prefix:

curl -X GET "http://ha:8123/api/states" \
  -H "Authorization: ${HA_TOKEN}"  # Missing "Bearer "

✅ Correct - Bearer prefix required:

curl -X GET "http://ha:8123/api/states" \
  -H "Authorization: Bearer ${HA_TOKEN}"

Why: Home Assistant's API uses standard Bearer token authentication. The "Bearer " prefix tells the server this is a token-based auth scheme, not a username/password.

REST API Endpoints Reference

States Endpoint

Get all states:

GET /api/states
Authorization: Bearer {token}

Response (200 OK):

[
  {
    "entity_id": "light.living_room",
    "state": "on",
    "attributes": {
      "brightness": 255,
      "color_mode": "color_temp",
      "friendly_name": "Living Room Light"
    },
    "last_changed": "2025-12-31T18:00:00+00:00",
    "last_updated": "2025-12-31T18:05:00+00:00"
  }
]

Get single entity state:

GET /api/states/{entity_id}
Authorization: Bearer {token}

Create/update entity state:

POST /api/states/{entity_id}
Authorization: Bearer {token}
Content-Type: application/json

{
  "state": "on",
  "attributes": {
    "friendly_name": "Custom Entity",
    "custom_attribute": "value"
  }
}

Response (201 Created or 200 OK):

{
  "entity_id": "sensor.custom_sensor",
  "state": "on",
  "attributes": { ... }
}

Services Endpoint

Get all available services:

GET /api/services
Authorization: Bearer {token}

Response (200 OK):

[
  {
    "domain": "light",
    "services": {
      "turn_on": {
        "description": "Turn on light(s)",
        "fields": {
          "entity_id": {
            "description": "The entity_id of the light(s)",
            "example": ["light.living_room", "light.bedroom"]
          },
          "brightness": {
            "description": "Brightness 0-255",
            "example": 180
          }
        }
      },
      "turn_off": { ... }
    }
  }
]

Call a service:

POST /api/services/{domain}/{service}
Authorization: Bearer {token}
Content-Type: application/json

{
  "entity_id": "light.living_room",
  "brightness": 180,
  "transition": 2
}

Response (200 OK):

[
  {
    "entity_id": "light.living_room",
    "state": "on",
    "attributes": { ... }
  }
]

Events Endpoint

Get all events:

GET /api/events
Authorization: Bearer {token}

Fire an event:

POST /api/events/{event_type}
Authorization: Bearer {token}
Content-Type: application/json

{
  "custom_data": "value"
}

History Endpoint

Get entity history:

GET /api/history/period/{timestamp}?filter_entity_id={entity_id}
Authorization: Bearer {token}

Response (200 OK):

[
  [
    {
      "entity_id": "sensor.temperature",
      "state": "22.5",
      "attributes": { ... },
      "last_changed": "2025-12-31T12:00:00+00:00"
    }
  ]
]

Config Endpoint

Get Home Assistant configuration:

GET /api/config
Authorization: Bearer {token}

Response (200 OK):

{
  "latitude": 52.3,
  "longitude": 4.9,
  "elevation": 0,
  "unit_system": {
    "length": "km",
    "mass": "kg",
    "temperature": "°C",
    "volume": "L"
  },
  "time_zone": "Europe/Amsterdam",
  "components": ["light", "switch", "sensor", ...]
}

Template Endpoint

Render a template:

POST /api/template
Authorization: Bearer {token}
Content-Type: application/json

{
  "template": "{{ states('sensor.temperature') }}"
}

Response (200 OK):

{
  "template": "{{ states('sensor.temperature') }}",
  "result": "22.5"
}

WebSocket API Reference

Connection Flow

1. Open WebSocket connection to /api/websocket
2. Receive auth_required message (must respond within 10 seconds)
3. Send auth message with token
4. Receive auth_ok confirmation
5. Send subscriptions/commands
6. Receive responses and events in real-time

WebSocket Commands

Authentication:

// Message 1: Server sends (automatically)
{
  "type": "auth_required",
  "ha_version": "2025.1.0"
}

// Message 2: Client responds
{
  "type": "auth",
  "access_token": "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9..."
}

// Message 3: Server confirms
{
  "type": "auth_ok",
  "ha_version": "2025.1.0"
}

Subscribe to events:

{
  "id": 1,
  "type": "subscribe_events",
  "event_type": "state_changed"
}

// Responses come as:
{
  "id": 1,
  "type": "event",
  "event": {
    "type": "state_changed",
    "data": {
      "entity_id": "light.living_room",
      "old_state": { "state": "off", ... },
      "new_state": { "state": "on", ... }
    }
  }
}

Call a service:

{
  "id": 2,
  "type": "call_service",
  "domain": "light",
  "service": "turn_on",
  "service_data": {
    "entity_id": "light.living_room",
    "brightness": 200
  }
}

// Response:
{
  "id": 2,
  "type": "result",
  "success": true,
  "result": [
    {
      "entity_id": "light.living_room",
      "state": "on",
      "attributes": { ... }
    }
  ]
}

Get current states:

{
  "id": 3,
  "type": "get_states"
}

// Response:
{
  "id": 3,
  "type": "result",
  "success": true,
  "result": [ ... ]  // Array of all entity states
}

Subscribe to specific trigger:

{
  "id": 4,
  "type": "subscribe_trigger",
  "trigger": {
    "platform": "state",
    "entity_id": "light.living_room"
  }
}

// Trigger fires when light state changes:
{
  "id": 4,
  "type": "event",
  "event": { ... }
}

Code Examples

Python - REST API

import requests
import os

HA_URL = os.getenv("HA_URL", "http://localhost:8123")
HA_TOKEN = os.getenv("HA_TOKEN")

headers = {
    "Authorization": f"Bearer {HA_TOKEN}",
    "Content-Type": "application/json"
}

# Get all states
response = requests.get(f"{HA_URL}/api/states", headers=headers)
response.raise_for_status()
states = response.json()

# Get single entity
response = requests.get(f"{HA_URL}/api/states/light.living_room", headers=headers)
light_state = response.json()
print(f"Light state: {light_state['state']}")
print(f"Brightness: {light_state['attributes'].get('brightness', 'N/A')}")

# Call service
service_data = {
    "entity_id": "light.living_room",
    "brightness": 180,
    "transition": 2
}
response = requests.post(
    f"{HA_URL}/api/services/light/turn_on",
    headers=headers,
    json=service_data
)
response.raise_for_status()
print(f"Service call successful: {response.json()}")

# Handle errors
try:
    response = requests.get(f"{HA_URL}/api/states/invalid.entity", headers=headers)
    response.raise_for_status()
except requests.exceptions.HTTPError as e:
    if e.response.status_code == 401:
        print("ERROR: Token invalid or expired")
    elif e.response.status_code == 404:
        print("ERROR: Entity not found")
    else:
        print(f"ERROR: {e}")

Python - WebSocket API

import asyncio
import aiohttp
import json
import os

HA_URL = os.getenv("HA_URL", "http://localhost:8123").replace("http", "ws")
HA_TOKEN = os.getenv("HA_TOKEN")

async def monitor_light_changes():
    async with aiohttp.ClientSession() as session:
        async with session.ws_connect(f"{HA_URL}/api/websocket") as ws:
            # Wait for auth_required
            msg = await ws.receive_json()
            print(f"Server: {msg}")

            # Send auth
            await ws.send_json({
                "type": "auth",
                "access_token": HA_TOKEN
            })

            # Wait for auth_ok
            msg = await ws.receive_json()
            print(f"Server: {msg}")

            # Subscribe to state changes
            await ws.send_json({
                "id": 1,
                "type": "subscribe_events",
                "event_type": "state_changed"
            })

            # Listen for events
            async for msg in ws:
                event = msg.json()
                if event.get("type") == "event":
                    data = event["event"]["data"]
                    print(f"Entity: {data['entity_id']}")
                    print(f"  Old state: {data['old_state']['state']}")
                    print(f"  New state: {data['new_state']['state']}")

# Run the monitoring loop
asyncio.run(monitor_light_changes())

JavaScript - REST API

const HA_URL = process.env.HA_URL || "http://localhost:8123";
const HA_TOKEN = process.env.HA_TOKEN;

const headers = {
  "Authorization": `Bearer ${HA_TOKEN}`,
  "Content-Type": "application/json"
};

// Get all states
async function getAllStates() {
  const response = await fetch(`${HA_URL}/api/states`, { headers });
  if (!response.ok) {
    throw new Error(`HTTP ${response.status}: ${response.statusText}`);
  }
  return response.json();
}

// Get single entity
async function getEntityState(entityId) {
  const response = await fetch(`${HA_URL}/api/states/${entityId}`, { headers });
  if (response.status === 404) {
    throw new Error(`Entity ${entityId} not found`);
  }
  if (!response.ok) {
    throw new Error(`HTTP ${response.status}`);
  }
  const state = await response.json();
  console.log(`${entityId}: ${state.state}`);
  console.log(`Attributes:`, state.attributes);
  return state;
}

// Call service
async function callService(domain, service, data) {
  const response = await fetch(
    `${HA_URL}/api/services/${domain}/${service}`,
    {
      method: "POST",
      headers,
      body: JSON.stringify(data)
    }
  );
  if (!response.ok) {
    const error = await response.text();
    throw new Error(`HTTP ${response.status}: ${error}`);
  }
  return response.json();
}

// Example usage
(async () => {
  try {
    const states = await getAllStates();
    console.log(`Found ${states.length} entities`);

    await getEntityState("light.living_room");

    const result = await callService("light", "turn_on", {
      entity_id: "light.living_room",
      brightness: 180
    });
    console.log("Service call successful");
  } catch (error) {
    console.error(error);
  }
})();

JavaScript - WebSocket API

const HA_URL = (process.env.HA_URL || "http://localhost:8123").replace(/^http/, "ws");
const HA_TOKEN = process.env.HA_TOKEN;

async function subscribeToStateChanges() {
  const ws = new WebSocket(`${HA_URL}/api/websocket`);

  return new Promise((resolve, reject) => {
    ws.onopen = () => console.log("WebSocket connected");

    ws.onmessage = (event) => {
      const msg = JSON.parse(event.data);
      console.log("Message:", msg);

      if (msg.type === "auth_required") {
        // Respond to auth challenge
        ws.send(JSON.stringify({
          type: "auth",
          access_token: HA_TOKEN
        }));
      } else if (msg.type === "auth_ok") {
        // Authentication successful, subscribe to events
        ws.send(JSON.stringify({
          id: 1,
          type: "subscribe_events",
          event_type: "state_changed"
        }));
      } else if (msg.type === "event" && msg.event?.type === "state_changed") {
        // Handle state change
        const data = msg.event.data;
        console.log(`${data.entity_id} changed:`);
        console.log(`  ${data.old_state.state} → ${data.new_state.state}`);
      }
    };

    ws.onerror = (error) => {
      console.error("WebSocket error:", error);
      reject(error);
    };

    ws.onclose = () => {
      console.log("WebSocket closed");
      resolve();
    };
  });
}

subscribeToStateChanges();

cURL - Common Operations

# Get all entities
curl -X GET "http://localhost:8123/api/states" \
  -H "Authorization: Bearer ${HA_TOKEN}"

# Get specific entity
curl -X GET "http://localhost:8123/api/states/light.living_room" \
  -H "Authorization: Bearer ${HA_TOKEN}"

# Turn on light with brightness
curl -X POST "http://localhost:8123/api/services/light/turn_on" \
  -H "Authorization: Bearer ${HA_TOKEN}" \
  -H "Content-Type: application/json" \
  -d '{
    "entity_id": "light.living_room",
    "brightness": 200,
    "transition": 2
  }'

# Turn off light
curl -X POST "http://localhost:8123/api/services/light/turn_off" \
  -H "Authorization: Bearer ${HA_TOKEN}" \
  -H "Content-Type: application/json" \
  -d '{"entity_id": "light.living_room"}'

# Set climate temperature
curl -X POST "http://localhost:8123/api/services/climate/set_temperature" \
  -H "Authorization: Bearer ${HA_TOKEN}" \
  -H "Content-Type: application/json" \
  -d '{
    "entity_id": "climate.living_room",
    "temperature": 21
  }'

# Get service schema
curl -X GET "http://localhost:8123/api/services/light" \
  -H "Authorization: Bearer ${HA_TOKEN}"

# Call automation
curl -X POST "http://localhost:8123/api/services/automation/trigger" \
  -H "Authorization: Bearer ${HA_TOKEN}" \
  -H "Content-Type: application/json" \
  -d '{"entity_id": "automation.my_automation"}'

# Render template
curl -X POST "http://localhost:8123/api/template" \
  -H "Authorization: Bearer ${HA_TOKEN}" \
  -H "Content-Type: application/json" \
  -d '{"template": "{{ states(\"sensor.temperature\") }}"}'

Known Issues Prevention

Error Handling Patterns

HTTP Status Codes

import requests

try:
    response = requests.get(f"{HA_URL}/api/states/{entity_id}", headers=headers)

    if response.status_code == 401:
        print("Token invalid/expired - create new token in HA UI")
    elif response.status_code == 403:
        print("Forbidden - token lacks necessary permissions")
    elif response.status_code == 404:
        print("Entity not found - check entity_id")
    elif response.status_code == 502:
        print("Home Assistant unavailable - check server status")
    elif response.status_code >= 500:
        print("Server error - try again later")
    else:
        response.raise_for_status()
        return response.json()
except requests.exceptions.ConnectionError:
    print("Cannot connect to Home Assistant - verify HA_URL and network")
except requests.exceptions.Timeout:
    print("Request timeout - Home Assistant is slow to respond")

WebSocket Error Handling

const ws = new WebSocket(wsUrl);

ws.onerror = (error) => {
  console.error("WebSocket error:", error);
  // Reconnect after delay
  setTimeout(connect, 5000);
};

ws.onmessage = (event) => {
  const msg = JSON.parse(event.data);

  if (msg.type === "result" && !msg.success) {
    console.error("Command failed:", msg.error);
  }
};

ws.onclose = () => {
  console.log("Connection closed");
  // Implement reconnection logic
  setTimeout(connect, 3000);
};

Bundled Resources

References

Located in references/:

• REST_API_REFERENCE.md - Complete REST endpoint documentation
• WEBSOCKET_API_REFERENCE.md - WebSocket command reference
• AUTHENTICATION.md - Auth token creation and security best practices
• SERVICE_CATALOG.md - Common services by domain

Note: For deep dives on specific topics, see the reference files above.

Dependencies

Required

Optional

Official Documentation

• Home Assistant REST API
• Home Assistant WebSocket API
• Home Assistant Authentication
• Home Assistant Integration API

Troubleshooting

Cannot authenticate - 401 Unauthorized

Symptoms: All API requests return 401, even with correct token.

Solution:

1. Verify token in Home Assistant (Settings → Developer Tools → States/Services)
2. Check Authorization header includes "Bearer " prefix
3. Create new token if old one expired
4. Ensure HA_URL and HA_TOKEN environment variables are set

echo $HA_TOKEN  # Verify token is set
echo $HA_URL    # Verify URL is correct (http not https)

WebSocket connection closes immediately

Symptoms: WebSocket connects then closes without response.

Solution:

1. Verify Home Assistant version supports WebSocket API (2021.1+)
2. Check firewall doesn't block WebSocket upgrade
3. Ensure auth response is sent within 10 seconds of auth_required
4. Use correct /api/websocket path, not /api/websocket/

// Incorrect path
ws = new WebSocket("ws://ha:8123/api/websocket/");

// Correct path
ws = new WebSocket("ws://ha:8123/api/websocket");

Entity states appear as wrong type

Symptoms: State should be "on"/"off" but appears as number or boolean.

Solution:

1. Check entity's integration configuration
2. Reload integration in Developer Tools
3. Verify template/custom component isn't converting type
4. State is always a string in API response; parse as needed

state = entity["state"]  # String: "on", "off", "123"
is_on = state == "on"   # Convert to boolean

# For numeric states
temperature = float(entity["state"])  # Convert to float

Service call fails but no error returned

Symptoms: Service call returns HTTP 200 but nothing happens.

Solution:

1. Verify service exists: GET /api/services/{domain}
2. Check required fields in service_data
3. Verify entity_id is in entity_ids list, not as separate parameter
4. Check entity supports service (light.turn_on won't work on switch)

# Correct - entity_id in service_data
curl -X POST "http://ha:8123/api/services/light/turn_on" \
  -d '{"entity_id": "light.living_room"}'

# Incorrect - entity_id as path parameter
curl -X POST "http://ha:8123/api/services/light/turn_on/light.living_room"

Setup Checklist

Before using this skill, verify:

• Home Assistant instance is running and accessible (test via browser)
• Created Long-Lived Access Token (Settings → My Home → Create Token)
• Token stored in environment variable (HA_TOKEN) or secure vault
• Home Assistant URL set correctly (HA_URL with http not https)
• Firewall allows API/WebSocket connections (ports 8123 or custom)
• Python packages installed if using Python examples (pip install requests aiohttp)
• Tested connectivity with simple curl/fetch request before building full integration