microsoft/autogen · error · ValueError

Invalid name: {name}. Name must be less than 64 characters.

Error message

Invalid name: {name}. Name must be less than 64 characters.

What it means

Length branch of assert_valid_name in the llama.cpp client: raised when the name matches the allowed charset but is longer than 64 characters. Names validated by this module are capped at 64 chars because that is the limit the llama-cpp backend enforces.

Source

Thrown at python/packages/autogen-ext/src/autogen_ext/models/llama_cpp/_llama_cpp_completion_client.py:79

def normalize_name(name: str) -> str:
    """
    LLMs sometimes ask functions while ignoring their own format requirements, this function should be used to replace invalid characters with "_".

    Prefer _assert_valid_name for validating user configuration or input
    """
    return re.sub(r"[^a-zA-Z0-9_-]", "_", name)[:64]


def assert_valid_name(name: str) -> str:
    """
    Ensure that configured names are valid, raises ValueError if not.

    For munging LLM responses use _normalize_name to ensure LLM specified names don't break the API.
    """
    if not re.match(r"^[a-zA-Z0-9_-]+$", name):
        raise ValueError(f"Invalid name: {name}. Only letters, numbers, '_' and '-' are allowed.")
    if len(name) > 64:
        raise ValueError(f"Invalid name: {name}. Name must be less than 64 characters.")
    return name


def convert_tools(
    tools: Sequence[Tool | ToolSchema],
) -> List[ChatCompletionTool]:
    result: List[ChatCompletionTool] = []
    for tool in tools:
        if isinstance(tool, Tool):
            tool_schema = tool.schema
        else:
            assert isinstance(tool, dict)
            tool_schema = tool

        result.append(
            ChatCompletionTool(
                type="function",
                function=ChatCompletionToolFunction(

View on GitHub (pinned to 027ecf0a37)

Solutions

1. Truncate to 64 characters when constructing names
2. Use _normalize_name for any LLM-supplied name — it truncates and sanitizes in one step
3. Prefer short hashed slugs for long identifiers

Example fix

# before
name = f"{namespace}_{role}_{uuid4()}_executor"  # >64 chars

# after
name = f"{namespace}_{role}_{uuid4().hex[:8]}_executor"[:64]

def truncate_name(name: str, limit: int = 64) -> str:
    return name[:limit]

def is_valid_name_len(name: str) -> bool:
    return len(name) <= 64

When it happens

Trigger: Auto-composed names (team + role + task id) exceeding 64 characters passed as message sources or tool names to LlamaCppChatCompletionClient; long function names generated by an LLM and passed through unmodified.

Common situations: Deterministic name builders in orchestration frameworks; names derived from prompts or file paths; concatenating namespaces into tool names.

Related errors

• Invalid name: {name}. Only letters, numbers, '_' and '-' are
• Invalid name: {name}. Name must be less than 64 characters.
• Missing ANTHROPIC_API_KEY environment variable.
• The model does not support function calling.
• Unsupported tool type: {type(tool)}

AI-assisted analysis of microsoft/autogen@027ecf0a37 (2026-08-15). Data as JSON: /api/errors/34f94befaf740b57. Report an issue: GitHub.