microsoft/autogen · error · ValueError

Unknown content type from server: {type(content)}

Error message

Unknown content type from server: {type(content)}

What it means

Error "Unknown content type from server: {type(content)}" thrown in microsoft/autogen.

Source

Thrown at python/packages/autogen-ext/src/autogen_ext/tools/mcp/_workbench.py:358

                result_future = await self._actor.call("call_tool", {"name": original_name, "kargs": arguments})
                cancellation_token.link_future(result_future)
                result = await result_future
                assert isinstance(
                    result, CallToolResult
                ), f"call_tool must return a CallToolResult, instead of : {str(type(result))}"
                result_parts: List[TextResultContent | ImageResultContent] = []
                is_error = result.isError
                for content in result.content:
                    if isinstance(content, TextContent):
                        result_parts.append(TextResultContent(content=content.text))
                    elif isinstance(content, ImageContent):
                        result_parts.append(ImageResultContent(content=Image.from_base64(content.data)))
                    elif isinstance(content, EmbeddedResource):
                        # TODO: how to handle embedded resources?
                        # For now we just use text representation.
                        result_parts.append(TextResultContent(content=content.model_dump_json()))
                    else:
                        raise ValueError(f"Unknown content type from server: {type(content)}")
            except Exception as e:
                error_message = self._format_errors(e)
                is_error = True
                result_parts = [TextResultContent(content=error_message)]
        return ToolResult(name=name, result=result_parts, is_error=is_error)  # Return the requested name

    @property
    def initialize_result(self) -> Any:
        if self._actor:
            return self._actor.initialize_result

        return None

    async def list_prompts(self) -> ListPromptsResult:
        """List available prompts from the MCP server."""
        if not self._actor:
            await self.start()
        if self._actor is None:

View on GitHub (pinned to 027ecf0a37)

Solutions

1. Handle or filter the returned content type

Example fix

Convert the content to a supported type before processing

When it happens

Trigger: Thrown at python/packages/autogen-ext/src/autogen_ext/tools/mcp/_workbench.py:358 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of microsoft/autogen@027ecf0a37 (2026-08-15). Data as JSON: /api/errors/5637d531f3735f56. Report an issue: GitHub.