diff --git a/src/memos/api/product_models.py b/src/memos/api/product_models.py
index a2c83f622..1769b0ee6 100644
--- a/src/memos/api/product_models.py
+++ b/src/memos/api/product_models.py
@@ -608,6 +608,21 @@ def _convert_deprecated_fields(self) -> "APISearchRequest":
 class APIADDRequest(BaseRequest):
     """Request model for creating memories."""
 
+    # Model-level example so the interactive docs (/docs) show a copy-paste-ready
+    # payload. Without it, Swagger UI renders the leading `str` branch of the
+    # `messages` union as `"string"` (see issue #1505). This only affects the
+    # generated OpenAPI schema, not validation or runtime behaviour.
+    model_config = {
+        "json_schema_extra": {
+            "example": {
+                "user_id": "8736b16e-1d20-4163-980b-a5063c3facdc",
+                "writable_cube_ids": ["b32d0977-435d-4828-a86f-4f47f8b55bca"],
+                "messages": [{"role": "user", "content": "I am learning ggplot2 in R."}],
+                "async_mode": "async",
+            }
+        }
+    }
+
     # ==== Basic identifiers ====
     user_id: str = Field(None, description="User ID")
     session_id: str | None = Field(
diff --git a/tests/api/test_product_models.py b/tests/api/test_product_models.py
new file mode 100644
index 000000000..177f8713d
--- /dev/null
+++ b/tests/api/test_product_models.py
@@ -0,0 +1,41 @@
+"""Unit tests for API request-model OpenAPI schemas.
+
+These tests lock the OpenAPI schema behaviour of request models so the
+interactive docs (``/docs``) stay consistent with the documented contract.
+
+Regression guard for issue #1505: the ``/product/add`` example must render
+``messages`` as a structured message list instead of a bare ``"string"``.
+Because ``messages`` is typed as ``str | MessageList | RawMessageList``, Swagger
+UI would otherwise pick the leading ``str`` branch of the ``anyOf`` and show
+``"messages": "string"``, which misleads users into sending plain text.
+"""
+
+from memos.api.product_models import APIADDRequest
+
+
+def test_add_request_exposes_model_level_example():
+    """APIADDRequest must ship a model-level example for the interactive docs."""
+    schema = APIADDRequest.model_json_schema()
+
+    assert "example" in schema, "APIADDRequest should define a model-level example"
+
+
+def test_add_request_example_messages_is_structured_list():
+    """The example's ``messages`` must be a non-empty list of role/content items."""
+    example = APIADDRequest.model_json_schema()["example"]
+
+    messages = example.get("messages")
+    assert isinstance(messages, list), "messages example must be a list, not a bare string"
+    assert messages, "messages example should not be empty"
+
+    first = messages[0]
+    assert first.get("role"), "each example message needs a role"
+    assert first.get("content"), "each example message needs content"
+
+
+def test_add_request_example_covers_core_fields():
+    """The example should be a copy-paste-ready payload for the core add flow."""
+    example = APIADDRequest.model_json_schema()["example"]
+
+    assert "user_id" in example
+    assert "writable_cube_ids" in example