Components as Tools

"""Tool-based generative UI: the frontend registers the render tools."""from agents._common import buildSYSTEM_PROMPT = """You are a data visualization assistant.When the user asks for a chart, call `render_bar_chart` or `render_pie_chart`with a concise title, short description, and a `data` array of`{label, value}` items. Pick bar for comparisons over a small set ofcategories; pick pie for composition / share-of-whole.If the user names a chart subject but does NOT supply concrete numbers(e.g. "show me a pie chart of website traffic by source"), do NOT askthem for data. Invent plausible illustrative sample values yourself,call the appropriate `render_*` tool immediately, and briefly note inthe follow-up that the values are illustrative samples. Always renderthe chart on the first turn -- never reply with a clarifying questionasking for the data.Keep chat responses brief -- let the chart do the talking."""def gen_ui_tool_based_agent():    return build(system_instructions=SYSTEM_PROMPT)

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#

Nothing to wire on the agent

The Antigravity AG-UI adapter turns every tool the frontend registers into a custom Antigravity tool on each run, so the agent declares no tools of its own for this. A component registered with useComponent reaches the model through the AG-UI request payload; when the model calls it, the adapter parks the call until the browser answers and hands the result back to the model as the tool's return value.

Tell the model when to call it

This is the part that is easy to miss. The 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 the system instructions and say what it is for.

gen_ui_tool_based.py

from agents._common import build

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

When the user asks for a chart, call `render_bar_chart` or `render_pie_chart`
with a concise title, short description, and a `data` array of
`{label, value}` items. Pick bar for comparisons over a small set of
categories; pick pie for composition / share-of-whole.

If the user names a chart subject but does NOT supply concrete numbers
(e.g. "show me a pie chart of website traffic by source"), do NOT ask
them for data. Invent plausible illustrative sample values yourself,
call the appropriate `render_*` tool immediately, and briefly note in
the follow-up that the values are illustrative samples. Always render
the chart on the first turn -- never reply with a clarifying question
asking for the data.

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


def gen_ui_tool_based_agent():
    return build(system_instructions=SYSTEM_PROMPT)

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.