useAgent

import { useAgent } from "@copilotkit/react-core/v2";

function useAgent(options?: UseAgentProps): {
  agent: AbstractAgent;
  isReady: boolean;
};

Pass an empty array `[]` to prevent automatic re-renders.

### Core Properties

<PropertyReference name="agentId" type="string | undefined">
  Unique identifier for the agent instance.
</PropertyReference>

<PropertyReference name="description" type="string">
  Human-readable description of the agent's purpose.
</PropertyReference>

<PropertyReference name="threadId" type="string">
  Unique identifier for the current conversation thread.
</PropertyReference>

<PropertyReference name="messages" type="Message[]">
  Array of conversation messages. Each message contains:
  - `id: string` - Unique message identifier
  - `role: "user" | "assistant" | "system"` - Message role
  - `content: string` - Message content
</PropertyReference>

<PropertyReference name="state" type="any">
  Shared state object synchronized between application and agent. Both can read and modify this state.
</PropertyReference>

<PropertyReference name="isRunning" type="boolean">
  Indicates whether the agent is currently executing.
</PropertyReference>

### Methods

<PropertyReference name="runAgent" type="(parameters?: RunAgentParameters, subscriber?: AgentSubscriber) => Promise<RunAgentResult>">
  Manually triggers agent execution. Resolves with a `RunAgentResult` (`{ result, newMessages }`) once the run finalizes. `result` is the final value of the run and `newMessages` are the messages produced during it.

  **Parameters:**
  - `parameters.forwardedProps?: any` - Data to pass to the agent execution context

  **Example:**
  ```tsx
  const { result, newMessages } = await agent.runAgent({
    forwardedProps: {
      command: { resume: "user response" }
    }
  });
  ```
</PropertyReference>

<PropertyReference name="setState" type="(newState: any) => void">
  Updates the shared state. Changes are immediately available to both application and agent.

  **Example:**
  ```tsx
  agent.setState({
    ...agent.state,
    theme: "dark"
  });
  ```
</PropertyReference>

<PropertyReference name="subscribe" type="(subscriber: AgentSubscriber) => { unsubscribe: () => void }">
  Subscribes to agent events. Returns cleanup function.

  **Subscriber Events:**
  - `onCustomEvent?: ({ event: { name: string, value: any } }) => void` - Custom events
  - `onRunStartedEvent?: () => void` - Agent execution starts
  - `onRunFinalized?: () => void` - Agent execution completes
  - `onStateChanged?: (state: any) => void` - State changes
  - `onMessagesChanged?: (messages: Message[]) => void` - Messages added/modified
</PropertyReference>

<PropertyReference name="addMessage" type="(message: Message) => void">
  Adds a single message to the conversation and notifies subscribers.
</PropertyReference>

<PropertyReference name="addMessages" type="(messages: Message[]) => void">
  Adds multiple messages to the conversation and notifies subscribers once.
</PropertyReference>

<PropertyReference name="setMessages" type="(messages: Message[]) => void">
  Replaces the entire message history with a new array of messages.
</PropertyReference>

<PropertyReference name="abortRun" type="() => void">
  Aborts the currently running agent execution.
</PropertyReference>

<PropertyReference name="clone" type="() => AbstractAgent">
  Creates a deep copy of the agent with cloned messages, state, and configuration.
</PropertyReference>

`agent` is always a fully-constructed instance, so calling its methods is
always safe. While `isReady` is `false`, the instance is a placeholder that
is swapped for the real agent once the runtime finishes syncing — at which
point `agent` changes reference and dependent effects re-run. Guard on
`isReady` when you only want to act against the real agent, e.g. subscribing
to run-lifecycle events you don't want to miss during the provisional
window.

function AgentStatus() {
  const { agent } = useAgent();

  return (
    <div>
      <div>Agent: {agent.agentId}</div>
      <div>Messages: {agent.messages.length}</div>
      <div>Running: {agent.isRunning ? "Yes" : "No"}</div>
    </div>
  );
}

function StateController() {
  const { agent } = useAgent();

  return (
    <div>
      <pre>{JSON.stringify(agent.state, null, 2)}</pre>
      <button onClick={() => agent.setState({ ...agent.state, count: 1 })}>
        Update State
      </button>
    </div>
  );
}

function EventListener() {
  const { agent, isReady } = useAgent();

  useEffect(() => {
    // Guard on `isReady` so the subscription lands on the real agent rather
    // than the provisional one shown while the runtime is still connecting.
    // Depending on `agent` re-subscribes automatically once the real agent
    // is bound.
    if (!isReady) return;

    const { unsubscribe } = agent.subscribe({
      onRunStartedEvent: () => console.log("Started"),
      onRunFinalized: () => console.log("Finished"),
    });

    return unsubscribe;
  }, [agent, isReady]);

  return null;
}

function MultiAgentView() {
  const { agent: primary } = useAgent({ agentId: "primary" });
  const { agent: support } = useAgent({ agentId: "support" });

  return (
    <div>
      <div>Primary: {primary.messages.length} messages</div>
      <div>Support: {support.messages.length} messages</div>
    </div>
  );
}

// Only re-render when messages change
function MessageCount() {
  const { agent } = useAgent({
    updates: [UseAgentUpdate.OnMessagesChanged],
  });

  return <div>Messages: {agent.messages.length}</div>;
}