microsoft/autogen · error · ValueError

The participant names must be unique.

Error message

The participant names must be unique.

What it means

Participant names must be unique inside a group chat team because names are used as topic types and message-routing keys. A duplicate name would make message delivery ambiguous, so the constructor rejects it immediately.

Source

Thrown at python/packages/autogen-agentchat/src/autogen_agentchat/teams/_group_chat/_base_group_chat.py:84

    def __init__(
        self,
        name: str,
        description: str,
        participants: List[ChatAgent | Team],
        group_chat_manager_name: str,
        group_chat_manager_class: type[SequentialRoutedAgent],
        termination_condition: TerminationCondition | None = None,
        max_turns: int | None = None,
        runtime: AgentRuntime | None = None,
        custom_message_types: List[type[BaseAgentEvent | BaseChatMessage]] | None = None,
        emit_team_events: bool = False,
    ):
        self._name = name
        self._description = description
        if len(participants) == 0:
            raise ValueError("At least one participant is required.")
        if len(participants) != len(set(participant.name for participant in participants)):
            raise ValueError("The participant names must be unique.")
        self._participants = participants
        self._base_group_chat_manager_class = group_chat_manager_class
        self._termination_condition = termination_condition
        self._max_turns = max_turns
        self._message_factory = MessageFactory()
        if custom_message_types is not None:
            for message_type in custom_message_types:
                self._message_factory.register(message_type)

        for agent in participants:
            if isinstance(agent, ChatAgent):
                for message_type in agent.produced_message_types:
                    try:
                        is_registered = self._message_factory.is_registered(message_type)  # type: ignore[reportUnknownArgumentType]
                        if issubclass(message_type, StructuredMessage) and not is_registered:
                            self._message_factory.register(message_type)  # type: ignore[reportUnknownArgumentType]
                    except TypeError:
                        # Not a class or not a valid subclassable type (skip)

View on GitHub (pinned to 027ecf0a37)

Solutions

1. Give each agent/team a distinct name: AssistantAgent("coder"), AssistantAgent("reviewer").
2. If generating in a loop, suffix with the index: AssistantAgent(f"worker_{i}").
3. Add a pre-construction check: names = [p.name for p in participants]; assert len(names) == len(set(names)).

Example fix

# before
team = SelectorGroupChat([AssistantAgent("agent"), AssistantAgent("agent")])

# after
team = SelectorGroupChat([AssistantAgent("researcher"), AssistantAgent("coder")])

names = [p.name for p in participants]
if len(names) != len(set(names)):
    dupes = {n for n in names if names.count(n) > 1}
    raise ValueError(f"duplicate participant names: {dupes}")
team = RoundRobinGroupChat(participants)

When it happens

Trigger: Passing two agents constructed with the same name: AssistantAgent("assistant", ...) twice, or an agent named identically to a nested Team participant. The constructor compares len(participants) against the set of participant.name values.

Common situations: Agents created in loops with template names (agent_0 style) where the index was lost; copying example code twice; a nested team whose internal name collides with a top-level agent.

Related errors

• At least one participant is required.
• Task list cannot be empty.
• The maximum number of turns must be greater than 0.
• All agents must have a name.
• All agents must have a unique name.

AI-assisted analysis of microsoft/autogen@027ecf0a37 (2026-08-15). Data as JSON: /api/errors/36b9de67d4021e93. Report an issue: GitHub.