BYOC — Hashbrown

"use client";import { CopilotKit } from "@copilotkit/react-core/v2";import { HashBrownDashboard } from "./hashbrown-renderer";import { Chat } from "./chat";export default function ByocHashbrownDemoPage() {  return (    <CopilotKit      runtimeUrl="/api/copilotkit-declarative-hashbrown"      agent="declarative-hashbrown-demo"    >      <HashBrownDashboard>        <div className="flex h-screen flex-col gap-3 p-6">          <header>            <h1 className="text-lg font-semibold">Declarative UI: Hashbrown</h1>            <p className="text-sm text-[var(--muted-foreground)]">              Streaming structured output via <code>@hashbrownai/react</code>.              The agent emits a catalog-constrained UI envelope that renders              progressively as data streams.            </p>          </header>          <div className="flex-1 overflow-hidden rounded-md border border-[var(--border)]">            <Chat />          </div>        </div>      </HashBrownDashboard>    </CopilotKit>  );}

You have a chat surface and you want the agent to draw a dashboard, not just describe one in prose. By the end of this guide, the agent will stream a structured output object, @hashbrownai/react's progressive JSON parser will hand each finished slice to your renderer as it arrives, and the user sees the dashboard fill in live.

When to use this#

• Streaming dashboards where partial state should render before the full payload arrives.
• Agents authoring structured UI where the output is JSON-shaped, not free text.
• Cases where you already use Hashbrown for UI generation elsewhere in your stack.

If you'd rather work with an explicit catalog of registered components rather than streaming a JSON tree, see the sibling page BYOC — JSON Render for the same scenario implemented with @json-render/react.

Frontend#

The integration point is <CopilotChat>'s messageView.assistantMessage slot. Replace the default assistant-message renderer with a Hashbrown-backed one, and the chat takes care of everything else:

import {
  CopilotKit,
  CopilotChat,
  useConfigureSuggestions,
} from "@copilotkit/react-core/v2";
import { HashBrownAssistantMessage } from "./hashbrown-renderer";

export default function ByocHashbrownDemo() {
  useConfigureSuggestions({
    suggestions: [
      { title: "Sales overview", message: "Show me a sales dashboard." },
      { title: "Region split", message: "Break down sales by region." },
    ],
    available: "always",
  });

  return (
    <CopilotKit runtimeUrl="/api/copilotkit-byoc-hashbrown" agent="byoc_hashbrown">
      <CopilotChat
        messageView={{ assistantMessage: HashBrownAssistantMessage }}
      />
    </CopilotKit>
  );
}

The custom renderer is where Hashbrown earns its keep. useJsonParser consumes the streaming text content of an assistant message and emits typed JSON values as they parse; useUiKit resolves component names against your catalog and renders them with their props:

import { useJsonParser, useUiKit } from "@hashbrownai/react";
import { MetricCard } from "./metric-card";
import { PieChart, BarChart } from "./charts";

const catalog = {
  MetricCard,
  PieChart,
  BarChart,
};

export function HashBrownAssistantMessage({ message }: { message: AssistantMessage }) {
  const parsed = useJsonParser(message.content ?? "");
  const ui = useUiKit({ catalog, value: parsed });
  return <div className="space-y-3">{ui}</div>;
}

Each component in the catalog is just a regular React component. The catalog acts as a typed allowlist: anything the agent emits that isn't in the catalog won't render, so the agent can't draw arbitrary HTML into the page.

Backend#

The agent's job is to stream structured output, not text. How you do that depends on your framework, but the shape is always the same: emit a JSON object at the top level of the assistant message, where each child references a component name and props matching the catalog.

{
  "type": "MetricCard",
  "title": "Total revenue",
  "value": 184302,
  "delta": 0.07
}

Or a tree:

{
  "type": "Stack",
  "children": [
    { "type": "MetricCard", "title": "Total revenue", "value": 184302 },
    { "type": "BarChart",   "data": [...] }
  ]
}

Hashbrown's parser tolerates partial JSON, so the user sees MetricCard resolve before BarChart even starts streaming.

Comparing the two BYOC patterns#

Both byoc-hashbrown and byoc-json-render solve the same problem (agent-authored structured UI, rendered through a typed catalog), with two different rendering libraries. Pick whichever you already use elsewhere — the agent contract is the same shape; the React glue is what changes.

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