Frontend Tools

What is this?#

Frontend tools enable you to define client-side functions that your agent can invoke, with execution happening entirely in the user's browser. When your agent calls a frontend tool, the logic runs on the client side, giving you direct access to the frontend environment.

This can be utilized to let your agent control the UI, power generative UI, or support Human-in-the-loop interactions.

In this guide, we cover the use of frontend tools driving and interacting with the UI.

When should I use this?#

Use frontend tools when you need your agent to interact with client-side primitives such as:

Reading or modifying React component state
Accessing browser APIs like localStorage, sessionStorage, or cookies
Triggering UI updates or animations
Interacting with third-party frontend libraries
Performing actions that require the user's immediate browser context

Implementation#

Run and connect your agent#

You'll need to run your agent and connect it to CopilotKit before proceeding. If you haven't done so already, you can follow the instructions in the Getting Started guide.

If you don't already have an agent, you can use the coagent starter as a starting point as this guide uses it as a starting point.

Create a frontend tool#

First, you'll need to create a frontend tool using the useFrontendTool hook. Here's a simple one to get you started that says hello to the user.

page.tsx

import { z } from "zod";
import { useFrontendTool } from "@copilotkit/react-core/v2"

export function Page() {
  // ...

  useFrontendTool({
    name: "sayHello",
    description: "Say hello to the user",
    parameters: z.object({
      name: z.string().describe("The name of the user to say hello to"),
    }),
    handler: async ({ name }) => {
      alert(`Hello, ${name}!`);
      return `Said hello to ${name}!`;
    },
  });

  // ...
}

Modify your server#

Now, we'll ensure your AG-UI server can receive and pass these frontend actions to your agent logic.

Create your AG-UI server#

Set up your AG-UI server to serve your agent. Frontend tools registered with useFrontendTool are automatically made available to your agent through the AG-UI protocol.

Program.cs

using Azure.AI.OpenAI;
using Azure.Identity;
using Microsoft.Agents.AI;
using Microsoft.Agents.AI.Hosting.AGUI.AspNetCore;

var builder = WebApplication.CreateBuilder(args);
builder.Services.AddAGUI();
var app = builder.Build();

string endpoint = builder.Configuration["AZURE_OPENAI_ENDPOINT"]!;
string deployment = builder.Configuration["AZURE_OPENAI_DEPLOYMENT_NAME"]!;

// Create the agent
var agent = new AzureOpenAIClient(new Uri(endpoint), new DefaultAzureCredential())
    .GetChatClient(deployment)
    .CreateAIAgent(name: "AGUIAssistant", instructions: "You are a helpful assistant.");

// Map the AG-UI endpoint
app.MapAGUI("/", agent);
await app.RunAsync();

agent/src/byo_agent.py

from __future__ import annotations
import os
from fastapi import FastAPI
from dotenv import load_dotenv
from agent_framework import Agent
from agent_framework import SupportsChatGetResponse
from agent_framework.azure import AzureOpenAIChatClient
from agent_framework.openai import OpenAIChatClient
from agent_framework.ag_ui import add_agent_framework_fastapi_endpoint
from azure.identity import DefaultAzureCredential

load_dotenv()

def _build_chat_client() -> SupportsChatGetResponse:
    if bool(os.getenv("AZURE_OPENAI_ENDPOINT")):
        return AzureOpenAIChatClient(
            credential=DefaultAzureCredential(),
            deployment_name=os.getenv("AZURE_OPENAI_CHAT_DEPLOYMENT_NAME", "gpt-5.4-mini"),
            endpoint=os.getenv("AZURE_OPENAI_ENDPOINT"),
        )
    if bool(os.getenv("OPENAI_API_KEY")):
        return OpenAIChatClient(
            model=os.getenv("OPENAI_CHAT_MODEL_ID", "gpt-5.4-mini"),
            api_key=os.getenv("OPENAI_API_KEY"),
        )
    raise RuntimeError("Set AZURE_OPENAI_* or OPENAI_API_KEY in agent/.env")

chat_client = _build_chat_client()
agent = Agent(
    name="AGUIAssistant",
    instructions="You are a helpful assistant.",
    client=chat_client,
)

app = FastAPI(title="AG-UI Server (Python)")
add_agent_framework_fastapi_endpoint(app=app, agent=agent, path="/")

Frontend tools registered with useFrontendTool are automatically forwarded to your agent by the AG-UI protocol. The agent can invoke them just like backend tools, but execution happens on the frontend.

Give it a try!#

You've now given your agent the ability to directly call any frontend tools you've defined. These tools will be available to the agent where they can be used as needed.