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Hook into the agent’s lifecycle to build custom experiences on top of Crow.

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Available Callbacks

CallbackFires when
onMessageA new message (user or assistant) is added
onMessageUpdateA message is updated (e.g. during streaming)
onToolCallA tool starts, completes, or a client tool is invoked
onWorkflowA workflow starts, progresses, or ends
onVerificationStatusIdentity verification status changes
onErrorAn error occurs

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React SDK

Pass callbacks via the client.on() method: 
import { CrowClient } from '@usecrow/client';

const client = new CrowClient({
  productId: 'YOUR_PRODUCT_ID',
  apiUrl: 'https://api.usecrow.org',
});

client.on({
  onMessage: (message) => {
    console.log(`[${message.role}] ${message.content}`);
  },

  onToolCall: (event) => {
    if (event.type === 'tool_call_start') {
      console.log(`Tool started: ${event.toolName}`);
    }
    if (event.type === 'tool_call_complete') {
      console.log(`Tool done: ${event.toolName}`, event.success);
    }
  },

  onError: (error) => {
    myErrorTracker.capture(error);
  },
});

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Callback Reference

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onMessage

onMessage?: (message: Message) => void
Fired when a new message is added to the conversation. 
interface Message {
  id: string;
  content: string;
  role: 'user' | 'assistant';
  timestamp: Date;
  citations?: Citation[];
  thinking?: string;
}

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onMessageUpdate

onMessageUpdate?: (messageId: string, updates: Partial<Message>) => void
Fired when a message is updated — typically during streaming as the assistant’s response accumulates.

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onToolCall

onToolCall?: (event: ToolCallEvent) => void
Fired on tool lifecycle events:
event.typeDescription
tool_call_startServer-side tool invocation began
tool_call_completeServer-side tool finished (event.success)
client_tool_callClient-side tool was invoked in the browser

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onWorkflow

onWorkflow?: (event: WorkflowEvent) => void
event.typeDescription
workflow_startedWorkflow began (event.name, event.todos)
workflow_todo_updatedA step completed (event.todoId, event.status)
workflow_endedWorkflow finished
workflow_complete_promptWorkflow requests user confirmation

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onVerificationStatus

onVerificationStatus?: (isVerified: boolean) => void
Fired when the user’s identity verification status changes — useful for gating features behind verified users.

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onError

onError?: (error: Error) => void
Fired on any error during streaming or tool execution.

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Use Cases

Analytics — Track which tools are used and how often: 
client.on({
  onToolCall: (event) => {
    if (event.type === 'tool_call_complete') {
      analytics.track('crow_tool_used', {
        tool: event.toolName,
        success: event.success,
      });
    }
  },
});
Custom loading states — Show your own UI while tools run: 
client.on({
  onToolCall: (event) => {
    if (event.type === 'tool_call_start') {
      showToolSpinner(event.toolName);
    }
    if (event.type === 'tool_call_complete') {
      hideToolSpinner();
    }
  },
});
Error reporting — Pipe errors to your observability stack: 
client.on({
  onError: (error) => {
    Sentry.captureException(error);
  },
});

Client Side Tools

Register browser-side tool handlers

Embed Widget

Install the widget