Agents

agent-colosseum ships with two built-in agents. You can also write your own.

Agent	Description
RandomAgent(agent_id, seed)	Picks a random allowed action each turn. Useful for testing and baselines.
LangChainNegotiationAgent	Game-agnostic LLM agent. You supply a system prompt; it receives game state and returns actions. Supports OpenAI and OpenRouter.

Agent interface

Method	Required	Description
agent_id (property)	Yes	Unique string identifier
act(state: TurnState) -> AgentResponse	Yes	Observe game state, return messages + one game action
on_match_start(match_id, game_id, agent_ids)	No	Called before a match begins
on_match_end(match_id, outcome)	No	Called after a match ends

Turn model

Each turn, the current agent receives a TurnState and returns an AgentResponse:

• Messages (AgentResponse.messages) are delivered first. They do not consume a turn. You can send zero or more messages per turn (capped by max_messages_per_turn).
• Action (AgentResponse.action) is the game action (e.g. submit_offer, accept, submit_bid). This advances the turn.
• message_only is a special action that does not advance the turn. When an agent uses it, the other agent is pinged to reply. This allows multi-turn chat before committing to a game action.