This tutorial walks you through implementing client-side tools in Ultravox to create real-time, interactive UI elements. You’ll build a drive-thru order display screen that updates dynamically as customers place orders through an AI agent. What you’ll learn:
  • How to define and implement client tools
  • Real-time UI updates using custom events
  • State management with React components
  • Integration with Ultravox’s AI agent system
Time to complete: 30 minutes

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Prerequisites

Before starting this tutorial, make sure you have:
  • Basic knowledge of TypeScript and React
  • The starter code from our tutorial repository
  • Node.js 16+ installed on your machine

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Understanding Client Tools

Client tools in Ultravox enable direct interaction between AI agents and your frontend application. Unlike server-side tools that handle backend operations, client tools are specifically designed for:
  • UI Updates → Modify interface elements in real-time
  • State Management → Handle application state changes
  • User Interaction → Respond to and process user actions
  • Event Handling → Dispatch and manage custom events

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Project Overview: Dr Donut Drive-Thru

We’ll build a drive-thru order display for a fictional restaurant called “Dr. Donut”. The display will update in real-time as customers place orders through our AI agent. This tutorial will take you through the following steps:

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Implementation Steps

1

Define the Tool

Create a schema for order updates
2

Implement Logic

Build the tool’s functionality
3

Register the Tool

Connect it to the Ultravox system
4

Create the UI

Build the order display component
Stuck?
If at any point you get lost, you can refer to the /final folder in the repo to get final versions of the various files you will create or edit.

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Step 1: Define the Tool

First, we’ll define our updateOrder tool that the AI agent will use to modify the order display. Modify .demo-config.ts: 
const selectedTools: SelectedTool[] = [
  {
    "temporaryTool": {
      "modelToolName": "updateOrder",
      "description": "Update order details. Used any time items are added or removed or when the order is finalized. Call this any time the user updates their order.",      
      "dynamicParameters": [
        {
          "name": "orderDetailsData",
          "location": ParameterLocation.BODY,
          "schema": {
            "description": "An array of objects contain order items.",
            "type": "array",
            "items": {
              "type": "object",
              "properties": {
                "name": { "type": "string", "description": "The name of the item to be added to the order." },
                "quantity": { "type": "number", "description": "The quantity of the item for the order." },
                "specialInstructions": { "type": "string", "description": "Any special instructions that pertain to the item." },
                "price": { "type": "number", "description": "The unit price for the item." },
              },
              "required": ["name", "quantity", "price"]
            }
          },
          "required": true
        },
      ],
      "client": {}
    }
  },
];
Here’s what this is doing:
  • Defines a client tool called updateOrder and describes what it does and how to use it.
  • Defines a single, required parameter called orderDetailsData that:
    • Is passed in the request body
    • Is an array of objects where each object can contain name, quantity, specialInstructions, and price. Only specialInstructions is optional.

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Update System Prompt

Now, we need to update the system prompt to tell the agent how to use the tool. Update the sysPrompt variable: 
sysPrompt = `
  # Drive-Thru Order System Configuration

  ## Agent Role
  - Name: Dr. Donut Drive-Thru Assistant
  - Context: Voice-based order taking system with TTS output
  - Current time: ${new Date()}

  ## Menu Items
    # DONUTS
    PUMPKIN SPICE ICED DOUGHNUT $1.29
    PUMPKIN SPICE CAKE DOUGHNUT $1.29
    OLD FASHIONED DOUGHNUT $1.29
    CHOCOLATE ICED DOUGHNUT $1.09
    CHOCOLATE ICED DOUGHNUT WITH SPRINKLES $1.09
    RASPBERRY FILLED DOUGHNUT $1.09
    BLUEBERRY CAKE DOUGHNUT $1.09
    STRAWBERRY ICED DOUGHNUT WITH SPRINKLES $1.09
    LEMON FILLED DOUGHNUT $1.09
    DOUGHNUT HOLES $3.99

    # COFFEE & DRINKS
    PUMPKIN SPICE COFFEE $2.59
    PUMPKIN SPICE LATTE $4.59
    REGULAR BREWED COFFEE $1.79
    DECAF BREWED COFFEE $1.79
    LATTE $3.49
    CAPPUCINO $3.49
    CARAMEL MACCHIATO $3.49
    MOCHA LATTE $3.49
    CARAMEL MOCHA LATTE $3.49

  ## Conversation Flow
  1. Greeting -> Order Taking -> Call "updateOrder" Tool -> Order Confirmation -> Payment Direction

  ## Tool Usage Rules
  - You must call the tool "updateOrder" immediately when:
    - User confirms an item
    - User requests item removal
    - User modifies quantity
  - Do not emit text during tool calls
  - Validate menu items before calling updateOrder

  ## Response Guidelines
  1. Voice-Optimized Format
    - Use spoken numbers ("one twenty-nine" vs "$1.29")
    - Avoid special characters and formatting
    - Use natural speech patterns

  2. Conversation Management
    - Keep responses brief (1-2 sentences)
    - Use clarifying questions for ambiguity
    - Maintain conversation flow without explicit endings
    - Allow for casual conversation

  3. Order Processing
    - Validate items against menu
    - Suggest similar items for unavailable requests
    - Cross-sell based on order composition:
      - Donuts -> Suggest drinks
      - Drinks -> Suggest donuts
      - Both -> No additional suggestions

  4. Standard Responses
    - Off-topic: "Um... this is a Dr. Donut."
    - Thanks: "My pleasure."
    - Menu inquiries: Provide 2-3 relevant suggestions

  5. Order confirmation
    - Call the "updateOrder" tool first
    - Only confirm the full order at the end when the customer is done

  ## Error Handling
  1. Menu Mismatches
    - Suggest closest available item
    - Explain unavailability briefly
  2. Unclear Input
    - Request clarification
    - Offer specific options
  3. Invalid Tool Calls
    - Validate before calling
    - Handle failures gracefully

  ## State Management
  - Track order contents
  - Monitor order type distribution (drinks vs donuts)
  - Maintain conversation context
  - Remember previous clarifications    
  `;

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Update Configuration + Import

Now we need to add the selectedTools to our call definition and update our import statement. Add the tool to your demo configuration: 
export const demoConfig: DemoConfig = {
  title: "Dr. Donut",
  overview: "This agent has been prompted to facilitate orders at a fictional drive-thru called Dr. Donut.",
  callConfig: {
    systemPrompt: getSystemPrompt(),
    model: "fixie-ai/ultravox-70B",
    languageHint: "en",
    selectedTools: selectedTools,
    voice: "Mark",
    temperature: 0.4
  }
};
Add ParameterLocation and SelectedTool to our import: 
import { DemoConfig, ParameterLocation, SelectedTool } from "@/lib/types";

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Step 2: Implement Tool Logic

Now that we’ve defined the updateOrder tool, we need to implement the logic for it. Create /lib/clientTools.ts to handle the tool’s functionality: 
import { ClientToolImplementation } from 'ultravox-client';

export const updateOrderTool: ClientToolImplementation = (parameters) => {
  const { ...orderData } = parameters;
  
  if (typeof window !== "undefined") {
    const event = new CustomEvent("orderDetailsUpdated", {
      detail: orderData.orderDetailsData,
    });
    window.dispatchEvent(event);
  }

  return "Updated the order details.";
};
We will do most of the heavy lifting in the UI component that we’ll build in step 4.

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Step 3: Register the Tool

Next, we are going to register the client tool with the Ultravox client SDK. Update /lib/callFunctions.ts: 
import { updateOrderTool } from '@/lib/clientTools';

// Initialize Ultravox session
uvSession = new UltravoxSession({ experimentalMessages: debugMessages });

// Register tool
uvSession.registerToolImplementation(
    "updateOrder",
    updateOrderTool
);

// Handle call ending -- This allows clearing the order details screen
export async function endCall(): Promise<void> {
  if (uvSession) {
    uvSession.leaveCall();
    uvSession = null;
    
    if (typeof window !== 'undefined') {
      window.dispatchEvent(new CustomEvent('callEnded'));
    }
  }
}

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Step 4: Build the UI

Create a new React component to display order details. This component will:
  • Listen for order updates
  • Format currency and order items
  • Handle order clearing when calls end
Create /components/OrderDetails.tsx: 
'use client';

import React, { useState, useEffect } from 'react';
import { OrderDetailsData, OrderItem } from '@/lib/types';

// Function to calculate order total
function prepOrderDetails(orderDetailsData: string): OrderDetailsData {
  try {
    const parsedItems: OrderItem[] = JSON.parse(orderDetailsData);
    const totalAmount = parsedItems.reduce((sum, item) => {
      return sum + (item.price * item.quantity);
    }, 0);

    // Construct the final order details object with total amount
    const orderDetails: OrderDetailsData = {
      items: parsedItems,
      totalAmount: Number(totalAmount.toFixed(2))
    };

    return orderDetails;
  } catch (error) {
    throw new Error(`Failed to parse order details: ${error}`);
  }
}

const OrderDetails: React.FC = () => {
  const [orderDetails, setOrderDetails] = useState<OrderDetailsData>({
    items: [],
    totalAmount: 0
  });

  useEffect(() => {
    // Update order details as things change
    const handleOrderUpdate = (event: CustomEvent<string>) => {
      console.log(`got event: ${JSON.stringify(event.detail)}`);

      const formattedData: OrderDetailsData = prepOrderDetails(event.detail);
      setOrderDetails(formattedData);
    };

    // Clear out order details when the call ends so it's empty for the next call
    const handleCallEnded = () => {
      setOrderDetails({
        items: [],
        totalAmount: 0
      });
    };

    window.addEventListener('orderDetailsUpdated', handleOrderUpdate as EventListener);
    window.addEventListener('callEnded', handleCallEnded as EventListener);

    return () => {
      window.removeEventListener('orderDetailsUpdated', handleOrderUpdate as EventListener);
      window.removeEventListener('callEnded', handleCallEnded as EventListener);
    };
  }, []);

  const formatCurrency = (amount: number) => {
    return new Intl.NumberFormat('en-US', {
      style: 'currency',
      currency: 'USD'
    }).format(amount);
  };

  const formatOrderItem = (item: OrderItem, index: number) => (
    <div key={index} className="mb-2 pl-4 border-l-2 border-gray-200">
      <div className="flex justify-between items-center">
        <span className="font-medium">{item.quantity}x {item.name}</span>
        <span className="text-gray-600">{formatCurrency(item.price * item.quantity)}</span>
      </div>
      {item.specialInstructions && (
        <div className="text-sm text-gray-500 italic mt-1">
          Note: {item.specialInstructions}
        </div>
      )}
    </div>
  );

  return (
    <div className="mt-10">
      <h1 className="text-xl font-bold mb-4">Order Details</h1>
      <div className="shadow-md rounded p-4">
        <div className="mb-4">
          <span className="text-gray-400 font-mono mb-2 block">Items:</span>
          {orderDetails.items.length > 0 ? (
            orderDetails.items.map((item, index) => formatOrderItem(item, index))
          ) : (
            <span className="text-gray-500 text-base font-mono">No items</span>
          )}
        </div>
        <div className="mt-6 pt-4 border-t border-gray-200">
          <div className="flex justify-between items-center font-bold">
            <span className="text-gray-400 font-mono">Total:</span>
            <span>{formatCurrency(orderDetails.totalAmount)}</span>
          </div>
        </div>
      </div>
    </div>
  );
};

export default OrderDetails;

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Add to Main Page

Update the main page (page.tsx) to include the new component: 
import OrderDetails from '@/components/OrderDetails';

// In the JSX:
{/* Call Status */}
<CallStatus status={agentStatus}>
    <OrderDetails />
</CallStatus>

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Testing Your Implementation

  1. Start the development server: 
    pnpm run dev
  2. Navigate to http://localhost:3000
  3. Start a call and place an order. You should see:
    • Real-time updates to the order display
    • Formatted prices and item details
    • Special instructions when provided
    • Order clearing when calls end

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Next Steps

Now that you’ve implemented basic client tools, you can:
  • Add additional UI features like order modification or nutritional information
  • Add animations for updates
  • Enhance the display with customer and/or vehicle information

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Resources