OpenBB-finance/OpenBB · error · ValueError

Argument name cannot be empty

Error message

Argument name cannot be empty

What it means

Pydantic field_validator error on ArgumentDefinitionModel: the 'name' field of an MCP prompt/tool argument definition was given an empty string. Argument names become template placeholders and keyword parameters, so an empty name is structurally invalid and is rejected at config-parse time before anything is constructed.

Source

Thrown at openbb_platform/extensions/mcp_server/openbb_mcp_server/models/mcp_config.py:55

class ArgumentDefinitionModel(BaseModel):
    """Model for validating prompt argument definitions."""

    name: str = Field(..., description="Name of the argument")
    type: str = Field(default="str", description="Type of the argument")
    default: Any | None = Field(
        default=None, description="Default value for the argument"
    )
    description: str | None = Field(
        default=None, description="Description of the argument"
    )

    @field_validator("name")
    @classmethod
    def validate_name(cls, v: str) -> str:
        """Validate argument name is a valid identifier."""
        if not v:
            raise ValueError("Argument name cannot be empty")
        if not re.match(r"^[a-zA-Z_][a-zA-Z0-9_]*$", v):
            raise ValueError(f"Argument name '{v}' must be a valid Python identifier")
        return v

    @field_validator("type")
    @classmethod
    def validate_type(cls, v: str) -> str:
        """Validate type is a recognized type string."""
        valid_types = {
            "str",
            "string",
            "int",
            "integer",
            "float",
            "bool",
            "boolean",
            "list",
            "dict",

View on GitHub (pinned to 3e071fcc2c)

Solutions

1. Give every argument a non-empty name in the config file.
2. Audit the arguments: list in your prompt config for empty entries and remove or fill them.
3. If generating configs in code, assert name truthiness before building the model.

Example fix

# before (config.yaml)
arguments:
  - name: ""
    type: str

# after
arguments:
  - name: symbol
    type: str

def validate_arguments(args: list[dict]) -> None:
    for a in args:
        if not a.get("name"):
            raise ValueError(f"argument with empty name: {a}")

import re

def has_valid_argument_names(args: list[dict]) -> bool:
    return all(isinstance(a.get("name"), str) and re.match(r"^[a-zA-Z_][a-zA-Z0-9_]*$", a["name"]) for a in args)

When it happens

Trigger: Loading an MCP config (YAML/JSON) where an argument entry has name: "" or name: null serialized as empty; programmatically generating argument definitions with a missing-name bug; templates that default name to an empty string.

Common situations: Hand-written MCP prompt configs with placeholder arguments; config generators iterating empty lists; YAML indentation putting the name key on the wrong node.

Related errors

• Type '{v}' not recognized. Valid types: {', '.join(sorted(va
• Prompt content cannot be empty
• Tag must be a string, got {type(tag)}
• Argument name '{v}' must be a valid Python identifier
• Unmatched braces in prompt content: {open_braces} opening, {

AI-assisted analysis of OpenBB-finance/OpenBB@3e071fcc2c (2026-08-14). Data as JSON: /api/errors/2e963c40dfb1a24b. Report an issue: GitHub.