diff --git a/frontend/src/types/cad.types.ts b/frontend/src/types/cad.types.ts
new file mode 100644
index 0000000..ced82a7
--- /dev/null
+++ b/frontend/src/types/cad.types.ts
@@ -0,0 +1,75 @@
+/**
+ * Shared CAD type definitions — single source of truth.
+ * Import from here instead of duplicating interfaces across services/components.
+ */
+
+export interface CADLayer {
+  id: string;
+  name: string;
+  visible: boolean;
+  locked: boolean;
+  color?: string;
+  lineType?: string;
+  transparency?: number;
+  sortOrder?: number;
+}
+
+export interface CADProperties {
+  fill?: string;
+  stroke?: string;
+  strokeWidth?: number;
+  rotation?: number;
+  lineType?: 'solid' | 'dashed' | 'dotted';
+  radius?: number;
+  x1?: number;
+  y1?: number;
+  x2?: number;
+  y2?: number;
+  points?: Array<{ x: number; y: number }>;
+  text?: string;
+  fontSize?: number;
+  startAngle?: number;
+  endAngle?: number;
+  [key: string]: unknown;
+}
+
+export interface CADElement {
+  id: string;
+  type: string;
+  layerId: string;
+  x: number;
+  y: number;
+  width: number;
+  height: number;
+  properties: CADProperties;
+}
+
+export interface ExportData {
+  version: string;
+  exportedAt: number;
+  projectMeta: Record<string, unknown>;
+  layers: CADLayer[];
+  elements: CADElement[];
+}
+
+export interface ImportData {
+  version: string;
+  exportedAt: number;
+  projectMeta: Record<string, unknown>;
+  layers: CADLayer[];
+  elements: CADElement[];
+}
+
+export interface ExportOptions {
+  includeHiddenLayers?: boolean;
+  includeInvisibleElements?: boolean;
+  pageSize?: 'a4' | 'a3' | 'letter';
+  landscape?: boolean;
+}
+
+/** Unified return type for all export functions. */
+export interface ExportResult {
+  success: boolean;
+  data?: string;
+  error?: string;
+}