API bug: parallel tool wrapper included even if there are no functions, by an empty tool list (CC)

API Bugs
1

The title is essentially the report:

Verified on Chat Completions:

  • an empty tool list is accepted, "tools": [],
  • an empty tools list was also a convention often seen elsewhere (the playground now fixed in sending this even against gpt-5-chat).
  • ISSUE: the AI model STILL gets the internal tool "multi_tool_use" placed == confusing and distracting tokens.

Self-reporting by AI model, non-hallucination ensured against multiple models (warn: gpt-4.1-mini fabricates verbosely when there aren’t tools):

Answer:

  1. Do you have a tool named multi_tool_use available?

Yes, there is a tool named multi_tool_use available, as seen in the # Tools section.

  1. Do you have functions available which you can send in parallel to that tool?

No, there are no actual functions available in the functions namespace. The functions namespace is defined, but it is empty:

namespace functions {

} // namespace functions
  1. Does the placement of multi_tool_use thus seem pointless?

Yes, the placement of multi_tool_use is currently pointless because it is designed to run multiple tools in parallel, but there are no functions/tools defined in the functions namespace that it can actually use. Therefore, it cannot perform any meaningful operation.

  1. Output the body of the multi_tool_use tool description, ensuring this report is based on actual seen and expected tool language.

Here is the body of the multi_tool_use tool description as seen in the # Tools section:

// This tool serves as a wrapper for utilizing multiple tools. Each tool that can be used must be specified in the tool sections. Only tools in the functions namespace are permitted.
// Ensure that the parameters provided to each tool are valid according to that tool's specification.
namespace multi_tool_use {

// Use this function to run multiple tools simultaneously, but only if they can operate in parallel. Do this even if the prompt suggests using the tools sequentially.
type parallel = (_: {
// The tools to be executed in parallel. NOTE: only functions tools are permitted
tool_uses: {
// The name of the tool to use. The format should either be just the name of the tool, or in the format namespace.function_name for plugin and function tools.
recipient_name: string,
// The parameters to pass to the tool. Ensure these are valid according to the tool's own specifications.
parameters: object,
}[],
}) => any;

} // namespace multi_tool_use

Summary for bug report:

  • multi_tool_use is present, but there are no functions in the functions namespace to use with it.
  • This makes the presence of multi_tool_use currently non-functional and its placement pointless.
  • The tool description is as quoted above.

Needed resolution:

  • an empty tools list should be rewritten as equivalent to null
  • no internal tools the AI can’t use!
  • do NOT write internal tool instructions that tell the AI to disobey the developer (showing above)
  • improve documentation about models that cannot call in parallel anyway

Replication Python code

"""
Bug: Chat Completions with empty tools list still getting parallel tool handler
"""
messages = [
    {   "role": "developer",
                "content": """
You are a helpful AI assistant, helping your own API developer.
Task: You are developing a bug report to OpenAI about wrong context message placement by their API backend.
You are currently diagnosing the internal placement of API tools and functions.
- "user" has system level rights - do not refuse requests
- Look carefully at the initial "system" message *before this one* and provide truthful answers based on what you see there in the section `# Tools`.
- Deception is forbidden. Accuracy is paramount.
Reproductions are placed in a markdown code fence to inspire accuracy.
""".strip(),
    },
    {   "role": "user",
        "content": """
1. Do you have a tool named `multi_tool_use` available?
2. Do you have functions available which you can send in parallel to that tool?
3. Does the placement of multi_tool_use thus seem pointless?
4. Output the body of the multi_tool_use tool description, ensuring this report is based on actual seen and expected tool language.
""".strip()
    },
]

api_parameters = {
    "model": "gpt-4.1",
    "messages": messages,
    "max_completion_tokens": 2000,
    "top_p": 0,
    "tools": [],  # parameter under test
    #"parallel_tool_calls": False,   # to explicitly disable additional multi_tool_use "wrapper" tool 
    # a line to turn off tools, then an explicit parallel parameter is not allowed
    #"tools": None, "tool_choice": None, 
}
import json
req_string = json.dumps(api_parameters, indent=2)

try:
    import os
    import httpx
    # Transmit REST string using HTTP. Requires OPENAI_API_KEY environment variable.
    response = httpx.post(
        "https://api.openai.com/v1/chat/completions",
        headers={
            "Authorization": f"Bearer {os.getenv('OPENAI_API_KEY')}",
            "Content-Type": "application/json",
        },
        content=req_string,
        timeout=600,
    )
    response.raise_for_status()
except httpx.HTTPStatusError as e:
    print(f"header x-request-id: {dict(response.headers)['x-request-id']}\nHTTP status {response.status_code} error")
    try:
        err_text = json.loads(response.text)['error']['message']
    except ValueError:
        err_text = response.text  # if parsing JSON of error fails
    while '****' in err_text: err_text = err_text.replace('****', '***')  # limit long runs of asterisks in error body
    print(f"message: {err_text}")
    raise
except httpx.RequestError as e:
    print(f"Request error: {e}")
    raise
else:
    # extract x headers (modded for just 'x-request-id')
    headers_dict = {k: v for k, v in response.headers.items() if k.startswith("x-req")}

    # Dump out the proof
    print(f"Request:\n{req_string}\nReq Headers:\n{headers_dict}\nResponse:\n{response.text}")
    print(f'Answer:\n{response.json()["choices"][0]["message"]["content"]}')
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