diff --git a/src/lib/utils/yaml.ts b/src/lib/utils/yaml.ts
index fc64afbd..0e4aa8c7 100644
--- a/src/lib/utils/yaml.ts
+++ b/src/lib/utils/yaml.ts
@@ -56,7 +56,7 @@ export async function parseYaml<T = unknown>(yamlString: string): Promise<T> {
 
 /**
  * Order DeviceType fields according to schema v1.0.0
- * Field order: slug, manufacturer, model, part_number, u_height, is_full_depth, is_powered,
+ * Field order: slug, manufacturer, model, part_number, u_height, slot_width, is_full_depth, is_powered,
  *              weight, weight_unit, airflow, front_image, rear_image, colour, category, tags,
  *              notes, serial_number, asset_tag, links, custom_fields, interfaces, power_ports,
  *              power_outlets, device_bays, inventory_items, subdevice_role, va_rating
@@ -72,6 +72,7 @@ function orderDeviceTypeFields(dt: DeviceType): Record<string, unknown> {
 
   // --- Physical Properties ---
   ordered.u_height = dt.u_height;
+  if (dt.slot_width !== undefined) ordered.slot_width = dt.slot_width;
   if (dt.is_full_depth !== undefined) ordered.is_full_depth = dt.is_full_depth;
   if (dt.is_powered !== undefined) ordered.is_powered = dt.is_powered;
   if (dt.weight !== undefined) ordered.weight = dt.weight;
@@ -118,7 +119,7 @@ function orderDeviceTypeFields(dt: DeviceType): Record<string, unknown> {
 
 /**
  * Order PlacedDevice fields according to schema v1.0.0
- * Field order: id, device_type, name, position, face, front_image, rear_image,
+ * Field order: id, device_type, name, position, face, slot_position, front_image, rear_image,
  *              parent_device, device_bay, notes, custom_fields
  */
 function orderPlacedDeviceFields(
@@ -132,6 +133,8 @@ function orderPlacedDeviceFields(
   if (device.name !== undefined) ordered.name = device.name;
   ordered.position = device.position;
   ordered.face = device.face;
+  if (device.slot_position !== undefined)
+    ordered.slot_position = device.slot_position;
 
   // --- Placement Image Override ---
   if (device.front_image !== undefined)
diff --git a/src/tests/yaml-roundtrip.test.ts b/src/tests/yaml-roundtrip.test.ts
new file mode 100644
index 00000000..f6a93886
--- /dev/null
+++ b/src/tests/yaml-roundtrip.test.ts
@@ -0,0 +1,41 @@
+import { describe, it, expect } from "vitest";
+import { serializeLayoutToYaml, parseLayoutYaml } from "$lib/utils/yaml";
+import {
+  createTestDevice,
+  createTestDeviceType,
+  createTestLayout,
+  createTestRack,
+} from "./factories";
+
+describe("YAML layout round-trip", () => {
+  it("preserves half-width slot width and slot position", async () => {
+    const halfWidth = createTestDeviceType({
+      slug: "half-width-device",
+      u_height: 1,
+      slot_width: 1,
+    });
+
+    const layout = createTestLayout({
+      racks: [
+        createTestRack({
+          id: "rack-1",
+          devices: [
+            createTestDevice({
+              id: "placed-1",
+              device_type: halfWidth.slug,
+              position: 10,
+              slot_position: "left",
+            }),
+          ],
+        }),
+      ],
+      device_types: [halfWidth],
+    });
+
+    const yaml = await serializeLayoutToYaml(layout);
+    const restored = await parseLayoutYaml(yaml);
+
+    expect(restored.device_types[0]?.slot_width).toBe(1);
+    expect(restored.racks[0]?.devices[0]?.slot_position).toBe("left");
+  });
+});