CopilotKit

useAgent

React hook for accessing AG-UI agent instances

Overview

useAgent is a React hook that returns an AG-UI AbstractAgent instance. The hook subscribes to agent state changes and triggers re-renders when the agent's state, messages, or execution status changes.

Throws an error if no agent is configured with the specified agentId, or if only part of the thread-scoped option set is provided.

Signature

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

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

For fully headless UI that does not import the built-in chat rendering stack, import the hook from the headless entry:

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

Two valid shapes

The options object admits exactly two shapes, and the type rejects everything in between:

// Bind to an agent — the shared instance from the registry. The thread comes
// from the surrounding chat configuration.
const { agent } = useAgent();
const { agent } = useAgent({ agentId: "default" });

// Bind a private agent to a thread — all three properties are required.
const { agent } = useAgent({
  agentId: "chat-1",          // local id to register the private agent under
  runtimeAgentId: "default",  // the runtime agent it routes to
  threadId: "thread-abc",     // the thread to pin it to
});

Partial combinations do not compile. useAgent({ agentId, threadId }), useAgent({ agentId, runtimeAgentId }) and useAgent({ runtimeAgentId, threadId }) are all type errors.

A runtime agent registered under a given id is a singleton. Writing a per-hook threadId straight onto it would let two useAgent calls that share an agentId clobber each other's thread, so scoping a thread requires a private agent to pin it to.

Use the second shape when several frontend agents — one per open thread, for instance — have to mount against a single runtime agent. runtimeAgentId registers a proxied agent through CopilotKitCore.registerProxiedAgent, so each hook gets its own instance instead of a shared one.

Parameters

Prop

Type

Return Value

Prop

Type

Usage

Basic Usage

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>
  );
}

Accessing and Updating State

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>
  );
}

Event Subscription

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;
}

Multiple Agents

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>
  );
}

Thread-scoped Agent

Use the thread-scoped form when one runtime agent needs multiple independent frontend instances, for example one per open conversation. The local agentId must be unique in the current provider.

function ThreadPreview({ threadId }: { threadId: string }) {
  const { agent, isReady } = useAgent({
    agentId: `preview-${threadId}`,
    runtimeAgentId: "support",
    threadId,
    throttleMs: 100,
  });

  if (!isReady) return <div>Loading...</div>;

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

Optimizing Re-renders

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

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

Behavior

  • Automatic Re-renders: Component re-renders when agent state, messages, or execution status changes (configurable via updates parameter)
  • Readiness: While the runtime is connecting, agent is a fully-constructed provisional stand-in and isReady is false; once the runtime syncs, agent swaps to the real instance and isReady becomes true. Guard on isReady for work that must target the real agent (e.g. one-time subscriptions)
  • Error Handling: Throws error if no agent exists with specified agentId
  • State Synchronization: State updates via setState() are immediately available to both app and agent
  • Event Subscriptions: Subscribe/unsubscribe pattern for lifecycle and custom events

Related