---
title: Tool Rendering
icon: "lucide/Server"
description: Render your agent's tool calls with custom UI components.
---

## What is this?

Tools are a way for the LLM to call predefined, typically, deterministic functions. CopilotKit allows you to render these tools in the UI
as a custom component, which we call **Generative UI**.

<Callout type="info">
  CopilotKit consumes AG-UI protocol events streamed by AG2 over{" "}
  <code>/chat</code>. See the{" "}
  <a href="https://docs.ag2.ai/latest/docs/user-guide/ag-ui/" target="_blank">
    AG2 AG-UI integration docs
  </a>
  .
</Callout>

## When should I use this?

Rendering tools in the UI is useful when you want to provide the user with feedback about what your agent is doing, specifically
when your agent is calling tools. CopilotKit allows you to fully customize how these tools are rendered in the chat.

## Implementation

<Steps>
<Step>
### Run and connect your agent
Start your AG2 backend with a `/chat` endpoint and connect CopilotKit to that endpoint.
</Step>
<Step>
### Give your agent a tool to call

<Tabs groupId="language_ag2_agent_backend_tools" items={['Python']} default="Python" persist>
    <Tab value="Python">
        ```python title="agent.py"
        from typing import Annotated

        from fastapi import FastAPI, Header
        from fastapi.responses import StreamingResponse
        from autogen import ConversableAgent, LLMConfig
        from autogen.ag_ui import AGUIStream, RunAgentInput

        agent = ConversableAgent(
            name="assistant",
            system_message="You are a helpful assistant.",
            llm_config=LLMConfig({"model": "gpt-5.4-mini"}),
        )

        @agent.register_for_llm(
            description="Get the weather for a given location. Ensure location is fully spelled out."
        )
        def get_weather(location: Annotated[str, "Fully spelled out location"]) -> str:
            return f"The weather in {location} is sunny."

        # Register the same function for execution on this backend process.
        agent.register_for_execution(name="get_weather")(get_weather)

        stream = AGUIStream(agent)
        app = FastAPI()

        @app.post("/chat")
        async def run_agent(
            message: RunAgentInput,
            accept: str | None = Header(None),
        ):
            return StreamingResponse(
                stream.dispatch(message, accept=accept),
                media_type=accept or "text/event-stream",
            )
        ```
    </Tab>

</Tabs>
</Step>
<Step>
### Render the tool call in your frontend
At this point, your agent will be able to call the `get_weather` tool. Now
we just need to add a `useRenderTool` hook to render the tool call in
the UI.

<Callout type="info" title="Important">
  In order to render a tool call in the UI, the name of the action must match
  the name of the tool.
</Callout>

```tsx title="app/page.tsx"
// ...

const YourMainContent = () => {
  // ...
  // [!code highlight:12]
  useRenderTool({
    name: "get_weather",
    render: ({ status, args }) => {
      return (
        <p className="text-gray-500 mt-2">
          {status !== "complete" && "Calling weather API..."}
          {status === "complete" &&
            `Called the weather API for ${args.location}.`}
        </p>
      );
    },
  });
  // ...
};
```

</Step>
<Step>
### Give it a try!

Try asking the agent to get the weather for a location. You should see the custom UI component that we added
render the tool call and display the arguments that were passed to the tool.

<video
  src="https://cdn.copilotkit.ai/docs/copilotkit/images/coagents/tool-based-gen-ui.mp4"
  className="rounded-lg shadow-xl"
  loop
  playsInline
  controls
  autoPlay
  muted
/>
</Step>
</Steps>

## Default Tool Rendering

<DefaultToolRendering />
