OpenBB-finance/OpenBB · error · ValueError

Prompt content cannot be empty

Error message

Prompt content cannot be empty

What it means

Pydantic validation error on PromptConfigModel.content: the prompt template is empty or only whitespace. Prompt content is the rendered message body sent to the model, so an empty template is meaningless and is rejected. It fires when a config entry has content: "", content: null coerced oddly, or a whitespace-only string.

Source

Thrown at openbb_platform/extensions/mcp_server/openbb_mcp_server/models/mcp_config.py:106

        default=None, description="Name of the prompt (auto-generated if not provided)"
    )
    description: str | None = Field(
        default=None, description="Description of the prompt"
    )
    content: str = Field(description="Template content with {variable} placeholders")
    arguments: list[ArgumentDefinitionModel] = Field(
        default_factory=list, description="Argument definitions for the prompt"
    )
    tags: list[str] = Field(
        default_factory=list, description="Tags for categorizing the prompt"
    )

    @field_validator("content")
    @classmethod
    def validate_content(cls, v: str) -> str:
        """Validate content is not empty and contains valid template syntax."""
        if not v.strip():
            raise ValueError("Prompt content cannot be empty")

        # Check for unmatched braces
        open_braces = v.count("{")
        close_braces = v.count("}")
        if open_braces != close_braces:
            raise ValueError(
                f"Unmatched braces in prompt content: {open_braces} opening, {close_braces} closing"
            )

        return v

    @field_validator("name")
    @classmethod
    def validate_name(cls, v: str | None) -> str | None:
        """Validate prompt name if provided."""
        if v is not None:
            if not v.strip():
                raise ValueError("Prompt name cannot be empty string")

View on GitHub (pinned to 3e071fcc2c)

Solutions

1. Provide non-empty prompt text under the content key.
2. For YAML block scalars, indent the template body under content: |.
3. If generating configs, skip or fail loudly when the rendered template is blank.

Example fix

# before (content is empty)
prompts:
  - name: greet
    content:

# after
prompts:
  - name: greet
    content: |
      Summarize the following data: {data}

def validate_prompts(prompts: list[dict]) -> None:
    for p in prompts:
        if not str(p.get("content", "")).strip():
            raise ValueError(f"prompt {p.get('name', '<unnamed>')} has empty content")

def has_nonempty_content(prompt_cfg: dict) -> bool:
    return bool(str(prompt_cfg.get("content", "")).strip())

When it happens

Trigger: Loading an MCP prompt config whose content key is blank or missing text; YAML multiline scalars that collapse to empty (e.g. content: | with nothing indented under it); generators emitting prompts with unfilled templates.

Common situations: YAML indentation errors emptying a block scalar; templating pipelines producing '' for all entries; configs split across files with content defined in the wrong node.

Related errors

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

AI-assisted analysis of OpenBB-finance/OpenBB@3e071fcc2c (2026-08-14). Data as JSON: /api/errors/ee0fd4049c6b50a2. Report an issue: GitHub.