Components as Tools

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#

Wire CopilotKit middleware into your agent

Deep Agents compile to LangGraph graphs, and CopilotKitMiddleware is the bridge. It reads the forwarded tools off the request and merges them into the tool list the model sees, so a component registered with useComponent only reaches the model when the middleware is present.

agent.py

from deepagents import create_deep_agent
from copilotkit import CopilotKitMiddleware

agent = create_deep_agent(
    model="openai:gpt-5.4",
    tools=[],  # Backend tools go here
    middleware=[CopilotKitMiddleware()],
    system_prompt=SYSTEM_PROMPT,
)

Without the middleware the run still completes, and the component never renders, because the model was never told the tool exists.

Tell the model when to call it

The forwarded tool arrives on every run, but a model with no instruction about it will answer in prose and never call it. Name the tool in system_prompt and say what it is for.

agent.py

SYSTEM_PROMPT = """
You are a data visualization assistant.

When the user asks for a chart, call `render_bar_chart` with a concise
title and a `data` array of `{label, value}` items.

Keep chat responses brief and let the chart do the talking.
"""

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.

Missing snippet

No demo found for deepagents::gen-ui-tool-based. Known demos are bundled from manifest demos[i]; check the cell id and framework slug.

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.