diff --git a/src/app/api/asset-category-attribute-defs/route.ts b/src/app/api/asset-category-attribute-defs/route.ts
new file mode 100644
index 0000000..297ea31
--- /dev/null
+++ b/src/app/api/asset-category-attribute-defs/route.ts
@@ -0,0 +1,59 @@
+import { NextResponse } from "next/server";
+import { auth } from "@/auth";
+import {
+  createAssetCategoryAttributeDef,
+  listAssetCategoryAttributeDefs,
+  validateCreateAssetCategoryAttributeDefInput,
+} from "@/lib/asset-category-attribute-defs";
+
+// Mirrors src/app/api/asset-categories/route.ts's pattern — middleware.ts
+// excludes /api from route protection, so this checks the session itself.
+// Flat permission model (CLAUDE.md): only "logged in or not", no role check.
+export async function POST(request: Request): Promise<NextResponse> {
+  const session = await auth();
+  if (!session) {
+    return NextResponse.json({ error: "Unauthorized" }, { status: 401 });
+  }
+
+  let body: unknown;
+  try {
+    body = await request.json();
+  } catch {
+    return NextResponse.json({ error: "Request body must be valid JSON" }, { status: 400 });
+  }
+
+  if (typeof body !== "object" || body === null) {
+    return NextResponse.json({ error: "Request body must be a JSON object" }, { status: 400 });
+  }
+
+  const { categoryId, key, label, dataType, required, sortOrder } =
+    body as Record<string, unknown>;
+  const validation = validateCreateAssetCategoryAttributeDefInput({
+    categoryId,
+    key,
+    label,
+    dataType,
+    required,
+    sortOrder,
+  });
+
+  if (!validation.ok) {
+    return NextResponse.json({ error: validation.error }, { status: 400 });
+  }
+
+  const created = await createAssetCategoryAttributeDef(validation.value);
+  if (!created.ok) {
+    return NextResponse.json({ error: created.error }, { status: 400 });
+  }
+  return NextResponse.json(created.value, { status: 201 });
+}
+
+export async function GET(): Promise<NextResponse> {
+  const session = await auth();
+  if (!session) {
+    return NextResponse.json({ error: "Unauthorized" }, { status: 401 });
+  }
+
+  const assetCategoryAttributeDefs = await listAssetCategoryAttributeDefs();
+  return NextResponse.json(assetCategoryAttributeDefs, { status: 200 });
+}