diff --git a/apps/api/config.py b/apps/api/config.py
new file mode 100644
index 0000000..a32f9d6
--- /dev/null
+++ b/apps/api/config.py
@@ -0,0 +1,146 @@
+"""Configuration loading and caching for API application.
+
+This module provides centralized configuration management for devices and layout,
+with startup validation and in-memory caching for performance.
+"""
+
+import logging
+from pathlib import Path
+from typing import Any
+
+import yaml
+
+from packages.home_capabilities.layout import UiLayout
+
+logger = logging.getLogger(__name__)
+
+# Global caches (loaded once at startup)
+devices_cache: list[dict[str, Any]] = []
+layout_cache: UiLayout | None = None
+
+
+def load_devices_from_file() -> list[dict[str, Any]]:
+    """Load devices from configuration file and validate.
+    
+    Returns:
+        list: List of device configurations
+        
+    Raises:
+        FileNotFoundError: If devices.yaml doesn't exist
+        KeyError: If any device is missing required homekit_aid field
+        ValueError: If devices.yaml is invalid or contains duplicate homekit_aid values
+    """
+    config_path = Path(__file__).parent.parent.parent / "config" / "devices.yaml"
+    
+    if not config_path.exists():
+        raise FileNotFoundError(f"devices.yaml not found at {config_path}")
+    
+    with open(config_path, "r") as f:
+        config = yaml.safe_load(f)
+    
+    if not config or "devices" not in config:
+        raise ValueError("devices.yaml must contain 'devices' key")
+    
+    # Normalize device entries: accept both 'id' and 'device_id', use 'device_id' internally
+    devices = config.get("devices", [])
+    for device in devices:
+        device["device_id"] = device.pop("device_id", device.pop("id", None))
+        
+        # Validate required homekit_aid field
+        if "homekit_aid" not in device:
+            raise KeyError(f"Device {device.get('device_id', 'unknown')} is missing required 'homekit_aid' field")
+    
+    # Validate unique homekit_aid values
+    aids = [d["homekit_aid"] for d in devices]
+    if len(aids) != len(set(aids)):
+        duplicates = [aid for aid in aids if aids.count(aid) > 1]
+        raise ValueError(f"Duplicate homekit_aid values found: {set(duplicates)}")
+    
+    logger.info(f"Loaded {len(devices)} devices with unique homekit_aid values (range: {min(aids)}-{max(aids)})")
+    
+    return devices
+
+
+def load_layout_from_file() -> UiLayout:
+    """Load UI layout from configuration file and validate.
+    
+    Returns:
+        UiLayout: Parsed and validated layout configuration
+        
+    Raises:
+        FileNotFoundError: If layout.yaml doesn't exist
+        ValueError: If layout validation fails
+        yaml.YAMLError: If YAML parsing fails
+    """
+    config_path = Path(__file__).parent.parent.parent / "config" / "layout.yaml"
+    
+    if not config_path.exists():
+        raise FileNotFoundError(
+            f"Layout configuration not found: {config_path}. "
+            f"Please create a layout.yaml file with room and device definitions."
+        )
+    
+    try:
+        with open(config_path, "r", encoding="utf-8") as f:
+            data = yaml.safe_load(f)
+    except yaml.YAMLError as e:
+        raise yaml.YAMLError(f"Failed to parse YAML in {config_path}: {e}")
+    
+    if data is None:
+        raise ValueError(f"Layout file is empty: {config_path}")
+    
+    try:
+        layout = UiLayout(**data)
+    except Exception as e:
+        raise ValueError(f"Invalid layout configuration in {config_path}: {e}")
+    
+    total_devices = layout.total_devices()
+    room_names = [room.name for room in layout.rooms]
+    logger.info(
+        f"Loaded layout: {len(layout.rooms)} rooms, "
+        f"{total_devices} total devices (Rooms: {', '.join(room_names)})"
+    )
+    
+    return layout
+
+
+def load_devices() -> list[dict[str, Any]]:
+    """Get devices from in-memory cache.
+    
+    Returns:
+        list: List of device configurations (loaded at startup)
+    """
+    return devices_cache
+
+
+def load_layout() -> UiLayout:
+    """Get layout from in-memory cache.
+    
+    Returns:
+        UiLayout: Layout configuration (loaded at startup)
+        
+    Raises:
+        RuntimeError: If layout cache is not initialized
+    """
+    if layout_cache is None:
+        raise RuntimeError("Layout cache not initialized. Application startup may have failed.")
+    return layout_cache
+
+
+def initialize_config() -> None:
+    """Initialize configuration by loading devices and layout.
+    
+    This function should be called once during application startup.
+    
+    Raises:
+        Exception: If configuration loading or validation fails
+    """
+    global devices_cache, layout_cache
+    
+    # Load devices with validation
+    devices_cache = load_devices_from_file()
+    
+    # Load layout with validation
+    layout_cache = load_layout_from_file()
+    
+    logger.info("Configuration initialization complete")