Components as Tools

"use client";import React from "react";import {  CopilotChat,  CopilotKit,  useComponent,} from "@copilotkit/react-core/v2";import { BarChart, barChartPropsSchema } from "./bar-chart";import { PieChart, pieChartPropsSchema } from "./pie-chart";import { useSuggestions } from "./suggestions";function Chat() {  useComponent({    name: "render_bar_chart",    description: "Display a bar chart with labeled numeric values.",    parameters: barChartPropsSchema,    render: BarChart,  });  useComponent({    name: "render_pie_chart",    description: "Display a pie chart with labeled numeric values.",    parameters: pieChartPropsSchema,    render: PieChart,  });  useSuggestions();  return (    <div className="flex justify-center items-center h-screen w-full">      <div className="h-full w-full max-w-4xl">        <CopilotChat          agentId="gen-ui-tool-based"          className="h-full rounded-2xl"        />      </div>    </div>  );}export default function ControlledGenUiDemo() {  return (    <CopilotKit runtimeUrl="/api/copilotkit" agent="gen-ui-tool-based">      <Chat />    </CopilotKit>  );}

What is this?#

Tool-based Generative UI is the simplest form of Generative UI: you register a React component with useComponent, and CopilotKit exposes it to the agent as a tool. When the agent calls the tool, CopilotKit renders your component inline in the chat, passing the tool's arguments straight through as typed props.

Unlike tool rendering, which wraps a real backend tool in a custom UI, tool-based GenUI is the component. There is no handler, no user interaction, no server-side execution. The agent decides when to show it, populates the data, and CopilotKit paints it.

When should I use this?#

Use useComponent when you want to:

Display rich UI (cards, charts, tables, dashboards) inline in the chat
Show structured data the agent has derived from its reasoning
Render previews, status indicators, or visual summaries
Let the agent present information beyond plain text

For components that need user interaction, see Human-in-the-loop. For operational transparency around a real backend tool, see Tool rendering.

How it works in code#

Take the forwarded tools off the Flow's state

A Flow owns its own model call, so unlike a chat agent it has to hand the forwarded tools to the model itself. Type the Flow on CopilotKitState and read state.copilotkit.actions — that is where a component registered with useComponent arrives.

src/agents/chart_flow.py

from crewai.flow.flow import Flow, start
from litellm import acompletion

from ag_ui_crewai import CopilotKitState, copilotkit_stream


class ChartFlow(Flow[CopilotKitState]):
    @start()
    async def chat(self) -> None:
        actions = self.state.copilotkit.actions or None
        response = await copilotkit_stream(
            await acompletion(
                model="openai/gpt-5-mini",
                messages=[
                    {"role": "system", "content": SYSTEM_PROMPT},
                    *self.state.messages,
                ],
                tools=actions,
                parallel_tool_calls=False,
                stream=True,
            )
        )
        self.state.messages.append(response.choices[0].message)

Wrap the call in copilotkit_stream so the tool call reaches the browser as it streams. A Flow that returns only when the model is finished renders nothing until the turn ends.

Decide when the component is required

The Flow controls tool_choice, which is the lever a chat agent does not have. Forcing the call on the user's turn and leaving it on auto afterwards is what renders the component immediately and still lets the run end: the follow-up turn is plain narration once the browser has returned the result.

src/agents/chart_flow.py

on_user_turn = bool(
    self.state.messages and self.state.messages[-1].get("role") == "user"
)
tool_choice = "required" if actions and on_user_turn else "auto"

Leaving tool_choice on auto for every turn is the usual reason a Flow answers in prose and the component never appears.

Import the React hook and Zod in the component that registers the tool. This also applies to the built-in agent, which needs no backend tool-registration step.

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

useComponent takes a name, a Zod schema for its props, and the component to render. The runtime registers it as a frontend tool so the agent can discover it, and the schema becomes that tool's parameter definition — it is what tells the model which arguments to send.

parameters is optional, but leaving it out advertises the tool with an empty parameter schema ({ "type": "object", "properties": {} }). The model then has nothing to fill in, so it calls the tool with no arguments and your component renders with no props. Pass a schema for any component that needs data.

page.tsx

  useComponent({    name: "render_bar_chart",    description: "Display a bar chart with labeled numeric values.",    parameters: barChartPropsSchema,    render: BarChart,  });

The component itself is ordinary React: it reads only its props and can stream in as the agent fills the payload. The example above uses Recharts for the bar chart; it doesn't know anything about CopilotKit.

The name you pass to useComponent is what the agent sees as the tool name. Make it a verb like render_bar_chart or show_weather so the LLM reliably picks it when the user asks for that visualization.

Rendering in a headless chat#

CopilotKit's built-in chat components paint registered components for you. A headless or custom chat renders the message list itself, so nothing paints a tool call unless you render it — the component is registered and the agent calls it, but the chat stays empty.

Render the tool calls on each assistant message with CopilotChatToolCallsView:

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

<CopilotChatToolCallsView message={assistantMessage} messages={allMessages} />;

It looks up the sibling tool-role message for each tool call and hands both to the registered renderer. For finer placement, call useRenderToolCall() and paint each tool call yourself — see Headless UI.