microsoft/autogen · error · UnsupportedKeywordError

Unsupported or missing item type `{item_type_name}` for arra

Error message

Unsupported or missing item type `{item_type_name}` for array field `{key}` in `{model_name}`

What it means

Error "Unsupported or missing item type `{item_type_name}` for array field `{key}` in `{model_name}`" thrown in microsoft/autogen.

Source

Thrown at python/packages/autogen-core/src/autogen_core/utils/_json_to_pydantic.py:277

        elif json_type == "array":
            if "minItems" in value:
                constraints["min_length"] = value["minItems"]
            if "maxItems" in value:
                constraints["max_length"] = value["maxItems"]
            item_schema = value.get("items", {"type": "string"})
            if "$ref" in item_schema:
                item_type = self.get_ref(item_schema["$ref"].split("/")[-1])
            elif item_schema.get("type") == "object" and "properties" in item_schema:
                # Handle array items that are objects with properties - create a nested model
                # Use hash-based naming to keep names short and unique
                item_model_name = self._get_item_model_name(key, model_name)
                item_type = self._json_schema_to_model(item_schema, item_model_name, root_schema)
            else:
                item_type_name = item_schema.get("type")
                if item_type_name is None:
                    item_type = str
                elif item_type_name not in TYPE_MAPPING:
                    raise UnsupportedKeywordError(
                        f"Unsupported or missing item type `{item_type_name}` for array field `{key}` in `{model_name}`"
                    )
                else:
                    item_type = TYPE_MAPPING[item_type_name]

            base_type = conlist(item_type, **constraints) if constraints else List[item_type]  # type: ignore[valid-type]

        if "format" in value:
            format_type = FORMAT_MAPPING.get(value["format"])
            if format_type is None:
                raise FormatNotSupportedError(f"Unknown format `{value['format']}` for `{key}` in `{model_name}`")
            if not isinstance(format_type, type):
                return format_type
            if not issubclass(format_type, str):
                return format_type
            return format_type

        return base_type

View on GitHub (pinned to 027ecf0a37)

Solutions

1. Define a supported items type

Example fix

Set 'items': {'type': 'string'} (or other supported type)

When it happens

Trigger: Thrown at python/packages/autogen-core/src/autogen_core/utils/_json_to_pydantic.py:277 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/c77146d10b98bce6. Report an issue: GitHub.