fix(proxy): count tool array fields that declare no items in the local estimate

litellm/litellm_core_utils/token_counter.py

@@ -1033,8 +1033,7 @@ 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)}[]"
+        return f"{_format_type(props.get('items', {}), indent)}[]"
     elif type == "object":
         return f"{{\n{_format_object_parameters(props, indent + 2)}\n}}"
     elif type in ["integer", "number"]:

tests/unit/litellm_core_utils/test_token_counter.py

@@ -1565,6 +1565,21 @@ def test_token_counter_uses_the_tokenizer_of_each_model_family_and_of_a_custom_t
     }
 
 
+def test_token_counter_counts_array_parameter_without_items():
+    messages = [{"role": "user", "content": "tag this"}]
+    tags_tool = {
+        "type": "function",
+        "function": {
+            "name": "set_tags",
+            "parameters": {"type": "object", "properties": {"tags": {"type": "array"}}, "required": ["tags"]},
+        },
+    }
+
+    assert token_counter(model="gpt-4o", messages=messages, tools=[tags_tool]) > token_counter(
+        model="gpt-4o", messages=messages
+    )
+
+
 class _Unprintable:
     def __str__(self) -> str:
         raise AssertionError("opaque block values must be dropped before they are serialized")
@@ -1608,6 +1623,7 @@ def test_uncountable_block_nesting_past_the_depth_limit_is_truncated():
     assert "leaf" not in text
 
 
+
 def test_uncountable_block_elides_inline_base64_data_but_keeps_plain_text_data():
     (message,) = messages_with_uncountable_blocks_as_text(
         [

tests/unit/proxy/test_proxy_token_counter.py

@@ -1382,3 +1382,25 @@ async def test_gemini_non_json_success_body_surfaces_as_bad_gateway_when_fallbac
         )
 
     assert exc_info.value.code == "502"
+
+
+@pytest.mark.asyncio
+async def test_local_estimate_counts_a_tool_with_an_array_property_without_items(monkeypatch):
+    monkeypatch.setattr(litellm.proxy.proxy_server, "llm_router", None)
+    tags_tool = {
+        "type": "function",
+        "function": {
+            "name": "set_tags",
+            "description": "Set tags",
+            "parameters": {"type": "object", "properties": {"tags": {"type": "array"}}, "required": ["tags"]},
+        },
+    }
+
+    async def count(tools: list[dict[str, object]] | None) -> int:
+        result = await token_counter(
+            request=TokenCountRequest(model="gpt-4o", messages=[{"role": "user", "content": "tag this"}], tools=tools)
+        )
+        return result.total_tokens
+
+    assert await count([tags_tool]) > await count(None)
+