diff --git a/app/agent/tools/impl/api.py b/app/agent/tools/impl/api.py
index 1e038cfbf..5a2c26fa9 100644
--- a/app/agent/tools/impl/api.py
+++ b/app/agent/tools/impl/api.py
@@ -16,6 +16,7 @@ from app.agent.policy.sanitizer import summarize_input
 from app.agent.tools.base import MoviePilotTool
 from app.agent.tools.result import inspect_tool_result
 from app.agent.tools.tags import ToolTag
+from app.schemas.common import JsonData
 from app.schemas.types import NotificationChannel
 
 _TOOL_MESSAGE_OPERATION_MAX_CHARS = 96
@@ -55,11 +56,13 @@ class MoviePilotApiInput(BaseModel):  # type: ignore[misc]
         default_factory=dict,
         description="Query-string fields declared by the selected operation.",
     )
-    body: Any = Field(
+    body: JsonData = Field(
         default=None,
         description=(
             "JSON request value declared by the selected operation and its loaded Skill contract. "
-            "Most operations use an object; a oneOf branch may require an exact scalar."
+            "Most operations use an object; a oneOf branch may require an exact scalar. "
+            "Keep objects and arrays, including nested file items, as native JSON values; "
+            "never JSON-encode them into strings."
         ),
     )
 
diff --git a/tests/test_agent_api_gateway.py b/tests/test_agent_api_gateway.py
index 6e2a6b2fd..874a009f9 100644
--- a/tests/test_agent_api_gateway.py
+++ b/tests/test_agent_api_gateway.py
@@ -194,6 +194,16 @@ def test_mcp_tools_list_preserves_all_moviepilot_api_operation_branches() -> Non
     assert operation_ids == set(API_OPERATION_ROUTES)
 
 
+def test_local_agent_tool_uses_the_same_precise_operation_schema() -> None:
+    """本地 Agent 绑定的工具 schema 至少必须提示 body 是 JSON 结构值。"""
+    tool = MoviePilotApiTool(session_id="session", user_id="api_user")
+    schema = tool.tool_call_schema
+    assert not isinstance(schema, dict)
+    body = schema.model_json_schema()["properties"]["body"]
+
+    assert body["$ref"].endswith("/JsonData")
+
+
 def test_mcp_collection_contract_distinguishes_exact_and_unavailable_totals() -> None:
     """MCP 必须说明缺省全量、精确总数和外部无总数三种集合语义。"""
     schema = MoviePilotApiTool(session_id="session", user_id="api_user").get_mcp_input_schema()