diff --git a/nextcloud_mcp_server/server/calendar.py b/nextcloud_mcp_server/server/calendar.py
index 8c7f939..0761a72 100644
--- a/nextcloud_mcp_server/server/calendar.py
+++ b/nextcloud_mcp_server/server/calendar.py
@@ -29,10 +29,14 @@ def _event_dict_to_summary(event: dict) -> CalendarEventSummary:
     else:
         categories = raw_categories
 
+    start = event.get("start_datetime", "")
+    if not start:
+        logger.debug("Event %s has no start_datetime", event.get("uid", "unknown"))
+
     return CalendarEventSummary(
         uid=event.get("uid", ""),
         summary=event.get("title", ""),
-        start=event.get("start_datetime", ""),
+        start=start,
         end=event.get("end_datetime"),
         all_day=event.get("all_day", False),
         location=event.get("location") or None,
@@ -240,7 +244,10 @@ def configure_calendar_tools(mcp: FastMCP):
                 limit=limit,
             )
 
-            # Enrich events with calendar context for per-event mapping
+            # Enrich events with calendar context for per-event mapping.
+            # Note: calendar_display_name is not available here without an
+            # extra list_calendars() call; the response-level calendar_name
+            # already identifies the calendar for single-calendar queries.
             for event in events:
                 event["calendar_name"] = calendar_name
 
@@ -463,6 +470,7 @@ def configure_calendar_tools(mcp: FastMCP):
                 end_datetime=end_datetime,
                 limit=limit,
             )
+            # calendar_display_name not available without extra API call
             for event in events:
                 event["calendar_name"] = calendar_name
         else:
diff --git a/nextcloud_mcp_server/server/contacts.py b/nextcloud_mcp_server/server/contacts.py
index dc44956..ca64af7 100644
--- a/nextcloud_mcp_server/server/contacts.py
+++ b/nextcloud_mcp_server/server/contacts.py
@@ -19,7 +19,13 @@ logger = logging.getLogger(__name__)
 
 
 def _raw_contact_to_model(raw: dict) -> Contact:
-    """Convert a raw contact dict from the contacts client to a Contact model."""
+    """Convert a raw contact dict from the contacts client to a Contact model.
+
+    Only maps fields the client's list_contacts() currently returns:
+    fullname, nickname, birthday, and email. Additional Contact model fields
+    (phones, addresses, organization, etc.) require expanding the client's
+    vCard parsing in ContactsClient.list_contacts().
+    """
     contact_info = raw.get("contact", {})
 
     # Convert email field (str, list, or None) to list[ContactField]
diff --git a/nextcloud_mcp_server/server/deck.py b/nextcloud_mcp_server/server/deck.py
index ee6f499..f48e134 100644
--- a/nextcloud_mcp_server/server/deck.py
+++ b/nextcloud_mcp_server/server/deck.py
@@ -107,7 +107,7 @@ def configure_deck_tools(mcp: FastMCP):
         )
         client = await get_client(ctx)
         board = await client.deck.get_board(board_id)
-        return [label.model_dump() for label in board.labels]
+        return [label.model_dump() for label in (board.labels or [])]
 
     @mcp.resource("nc://Deck/boards/{board_id}/labels/{label_id}")
     async def deck_label_resource(board_id: int, label_id: int):
@@ -209,7 +209,8 @@ def configure_deck_tools(mcp: FastMCP):
         """Get all labels in a Nextcloud Deck board"""
         client = await get_client(ctx)
         board = await client.deck.get_board(board_id)
-        return ListLabelsResponse(labels=board.labels, total=len(board.labels))
+        labels = board.labels or []
+        return ListLabelsResponse(labels=labels, total=len(labels))
 
     @mcp.tool(
         title="Get Deck Label",