fix: token_counter crashed on a tool array parameter without items

_format_type indexed props['items'] unguarded, so token_counter raised
KeyError('items') for any tool whose array-typed parameter omitted items, and
AttributeError when items was a list (JSON-Schema tuple validation). This is
token counting, not request validation, and the module degrades gracefully
elsewhere, so a missing or non-dict items should fall back to the generic any
type instead of raising. It is reachable through the public litellm.token_counter
API for both the OpenAI and Anthropic tool shapes.

litellm/litellm_core_utils/token_counter.py

@@ -814,8 +814,9 @@ def _format_type(props, indent):
             return " | ".join([f'"{item}"' for item in props["enum"]])
         return "string"
     elif type == "array":
-        # items is required, OpenAI throws an error if it's missing
-        return f"{_format_type(props['items'], indent)}[]"
+        items = props.get("items")
+        items = items if isinstance(items, dict) else {}
+        return f"{_format_type(items, indent)}[]"
     elif type == "object":
         return f"{{\n{_format_object_parameters(props, indent + 2)}\n}}"
     elif type in ["integer", "number"]:

tests/test_litellm/litellm_core_utils/test_token_counter.py

@@ -1114,3 +1114,53 @@ def test_count_content_list_rejects_unknown_type():
     message = str(exc_info.value)
     assert "Invalid content item type: totally_unknown_block" in message
     assert "tool_reference" in message
+
+
+@pytest.mark.parametrize(
+    "tools",
+    [
+        [
+            {
+                "type": "function",
+                "function": {
+                    "name": "f",
+                    "parameters": {
+                        "type": "object",
+                        "properties": {"tags": {"type": "array"}},
+                        "required": ["tags"],
+                    },
+                },
+            }
+        ],
+        [
+            {
+                "type": "function",
+                "function": {
+                    "name": "f",
+                    "parameters": {
+                        "type": "object",
+                        "properties": {"tags": {"type": "array", "items": [{"type": "string"}]}},
+                        "required": ["tags"],
+                    },
+                },
+            }
+        ],
+        [
+            {
+                "name": "f",
+                "input_schema": {
+                    "type": "object",
+                    "properties": {"tags": {"type": "array"}},
+                    "required": ["tags"],
+                },
+            }
+        ],
+    ],
+    ids=["openai_array_without_items", "openai_array_items_as_list", "anthropic_array_without_items"],
+)
+def test_token_counter_tool_array_param_missing_or_invalid_items(tools):
+    result = litellm.token_counter(
+        model="gpt-4o", messages=[{"role": "user", "content": "hi"}], tools=tools
+    )
+    assert isinstance(result, int)
+    assert result > 0