diff --git a/src/app/api/agent/cards/[cardId]/subtasks/route.ts b/src/app/api/agent/cards/[cardId]/subtasks/route.ts
new file mode 100644
index 0000000..a9d9ae2
--- /dev/null
+++ b/src/app/api/agent/cards/[cardId]/subtasks/route.ts
@@ -0,0 +1,68 @@
+import { getAdminPb } from "@/lib/pb/admin";
+import { requireAgentToken } from "@/lib/agent/auth";
+import { positionBetween } from "@/lib/ordering/fractional";
+import { jsonError, jsonOk } from "@/lib/http/json";
+import type { CardRecord, SubtaskRecord } from "@/lib/pb/types";
+
+/**
+ * POST /api/agent/cards/:cardId/subtasks — turn a plan into a checklist.
+ *
+ * Appends after the card's existing subtasks, in the order given, using the
+ * same fractional-position spacing every other subtask-creation path in this
+ * app uses (see addSubtask in src/app/actions/subtasks.ts).
+ */
+export async function POST(
+  request: Request,
+  context: { params: Promise<{ cardId: string }> }
+): Promise<Response> {
+  const denied = requireAgentToken(request);
+  if (denied) return denied;
+
+  const { cardId } = await context.params;
+
+  let json: unknown;
+  try {
+    json = await request.json();
+  } catch {
+    return jsonError("Invalid request body", 400);
+  }
+
+  const titles = (json as { titles?: unknown } | null)?.titles;
+  if (!Array.isArray(titles)) {
+    return jsonError("titles must be an array of strings", 400);
+  }
+
+  const cleaned = titles
+    .filter((t): t is string => typeof t === "string")
+    .map((t) => t.trim().slice(0, 200))
+    .filter((t) => t.length > 0);
+
+  if (cleaned.length === 0) {
+    return jsonError("At least one non-empty title is required", 400);
+  }
+
+  const pb = await getAdminPb();
+  const card = await pb.collection("cards").getOne<CardRecord>(cardId).catch(() => null);
+  if (!card || card.archived) return jsonError("Card not found", 404);
+
+  const last = await pb
+    .collection("subtasks")
+    .getFirstListItem<SubtaskRecord>(`card = "${cardId}"`, { sort: "-position" })
+    .catch(() => null);
+
+  let position: number | null = last ? last.position : null;
+  const created: string[] = [];
+
+  for (const title of cleaned) {
+    position = positionBetween(position, null);
+    const subtask = await pb.collection("subtasks").create({
+      card: cardId,
+      title,
+      done: false,
+      position,
+    });
+    created.push(subtask.id);
+  }
+
+  return jsonOk({ created }, 201);
+}