CopilotKit

Add a custom CopilotKit endpoint to a LangGraph deployment and render structured generative UI in React

CopilotKit provides a full React chat runtime and pairs especially well with LangGraph when you want the agent to return structured UI payloads instead of only plain text. In this pattern, your LangGraph deployment serves both the graph API and a custom CopilotKit endpoint, while the frontend parses assistant messages into dynamic React components.

This approach is useful when you want:

• a ready-made chat runtime instead of wiring stream.messages yourself
• a custom server endpoint that can add provider-specific behavior next to your deployed graph
• structured generative UI rendered from a constrained component registry

For CopilotKit-specific APIs, UI patterns, and runtime configuration, see the CopilotKit docs.

How it works

At a high level, CopilotKit sits between your React app and the LangGraph deployment. The frontend sends conversation state to a custom /api/copilotkit route mounted alongside the graph API, that route forwards the request to LangGraph, and the response comes back with both assistant messages and any structured UI payloads your component registry can render.

1. Deploy the graph as usual using LangSmith or using a LangGraph development server.
2. Extend the deployment with an HTTP app that mounts a CopilotKit route next to the graph API.
3. Wrap the frontend in CopilotKit and point it at that custom runtime URL.
4. Register dynamic UI components and parse assistant responses into those components at render time.

Installation

For the backend endpoint:

bun add @copilotkit/runtime hono

For the frontend app:

bun add @copilotkit/react-core @copilotkit/react-ui @hashbrownai/core @hashbrownai/react

Extend the LangGraph deployment with a custom endpoint

The key idea is that the LangGraph deployment does not only serve graphs. It can also load an HTTP app, which lets you mount extra routes next to the deployment itself.

In langgraph.json, point http.app at your custom app entrypoint:

{
  "graphs": {
    "copilotkit_shadify": "./src/agents/copilotkit-shadify.ts:agent"
  },
  "http": {
    "app": "./src/api/app.ts:app"
  }
}

Then create the Hono app and register the CopilotKit route:

app.ts

import { Hono } from "hono";
import { registerCopilotKit } from "./copilotkit.js";

export const app = new Hono();

registerCopilotKit(app);

This custom app is the important extension point: it mounts a CopilotKit-aware runtime without replacing the underlying LangGraph deployment.

Inside that route, create a CopilotRuntime and point it back at the deployed graph using LangGraphAgent:

copilotkit.ts

import { type Hono } from "hono";

import { createCopilotEndpointSingleRoute, CopilotRuntime } from "@copilotkit/runtime/v2";
import { LangGraphAgent } from "@copilotkit/runtime/langgraph";

const defaultAgentHost = process.env.LANGGRAPH_DEPLOYMENT_URL || "http://127.0.0.1:2024";
const agentUrl = defaultAgentHost.startsWith("http")
  ? defaultAgentHost
  : `http://${defaultAgentHost}`;

class BridgedLangGraphAgent extends LangGraphAgent {
  override prepareRunAgentInput(
    input: Parameters<LangGraphAgent["prepareRunAgentInput"]>[0],
  ): ReturnType<LangGraphAgent["prepareRunAgentInput"]> {
    const prepared = super.prepareRunAgentInput(input);

    return {
      ...prepared,
      context: normalizeCopilotContext(prepared.context) as ReturnType<
        LangGraphAgent["prepareRunAgentInput"]
      >["context"],
    };
  }

  override async getAssistant(): Promise<Awaited<ReturnType<LangGraphAgent["getAssistant"]>>> {
    const assistants = await this.client.assistants.search({
      graphId: this.graphId,
      limit: 100,
    });

    const assistant = assistants.find((candidate) => candidate.graph_id === this.graphId);
    if (assistant) {
      return assistant;
    }

    return super.getAssistant();
  }
}

export function registerCopilotKit(app: Hono) {
  const runtime = new CopilotRuntime({
    agents: {
      default: new BridgedLangGraphAgent({
        deploymentUrl: agentUrl,
        graphId: "copilotkit_shadify",
      }),
    },
  });

  const copilotApp = createCopilotEndpointSingleRoute({
    runtime,
    basePath: "/api/copilotkit",
  });

  app.route("/", copilotApp);
}

function normalizeCopilotContext(context: unknown): unknown {
  if (!Array.isArray(context)) {
    return context;
  }

  const normalizedEntries = context.flatMap((item) => {
    if (!item || typeof item !== "object") {
      return [];
    }

    const entry = item as { description?: unknown; value?: unknown };
    return typeof entry.description === "string" ? [[entry.description, entry.value] as const] : [];
  });

  return Object.fromEntries(normalizedEntries);
}

The route adapter is only half of the TypeScript setup. Your LangChain agent also needs middleware that reads the forwarded output_schema and turns it into a structured responseFormat for the model:

agent.ts

import { createAgent, createMiddleware, toolStrategy } from "langchain";
import { z } from "zod";

import { deepSearchTool, searchWebTool } from "../tools/index.js";

const contextSchema = z.object({
  output_schema: z.unknown().optional(),
});

const structuredOutputMiddleware = createMiddleware({
  name: "CopilotKitStructuredOutput",
  contextSchema,
  wrapModelCall: async (request, handler) => {
    const rawOutputSchema = getRuntimeOutputSchema(request.runtime);
    const schema = normalizeOutputSchema(rawOutputSchema);
    if (!schema) {
      return handler(request);
    }

    const responseFormat = toolStrategy(
      schema as unknown as Parameters<typeof toolStrategy>[0],
      {
        toolMessageContent: "Structured UI response generated.",
      },
    );

    return handler({
      ...request,
      responseFormat,
    });
  },
});

export const agent = createAgent({
  model: process.env.COPILOTKIT_MODEL ?? "google_genai:gemini-3.1-pro-preview",
  contextSchema,
  middleware: [structuredOutputMiddleware],
  tools: [searchWebTool, deepSearchTool],
  systemPrompt: `You are a helpful UI assistant inspired by the CopilotKit Shadify example.

Build rich visual responses with the available UI components when they add value.
Only wrap actual UI layouts inside cards. Plain Markdown answers should stay as Markdown.
Use rows for side-by-side layouts with at most two columns.
Prefer simple, polished outputs over dense dashboards.
When using charts, make labels and values concise and easy to read.
When showing code, prefer the code_block component.
When researching topics, use the available search tools first and then present the result cleanly.`,
});

function normalizeOutputSchema(value: unknown): Record<string, unknown> | null {
  let schema = value;

  if (typeof schema === "string") {
    try {
      schema = JSON.parse(schema);
    } catch {
      return null;
    }
  }

  if (!schema || typeof schema !== "object" || Array.isArray(schema)) {
    return null;
  }

  const normalized = { ...(schema as Record<string, unknown>) };

  if (!normalized.title) {
    normalized.title = "CopilotKitStructuredOutput";
  }

  if (!normalized.description) {
    normalized.description = "Structured response schema for the CopilotKit preview.";
  }

  return normalized;
}

function getRuntimeOutputSchema(runtime: {
  context?: { output_schema?: unknown };
  configurable?: Record<string, unknown>;
}): unknown {
  if (runtime.context?.output_schema !== undefined) {
    return runtime.context.output_schema;
  }

  const configurable = runtime.configurable;
  if (!configurable || typeof configurable !== "object" || Array.isArray(configurable)) {
    return undefined;
  }

  return configurable.output_schema;
}

This middleware is what makes useAgentContext({ description: "output_schema", ... }) useful on the frontend. The CopilotKit runtime forwards the schema, and the agent turns it into the structured output contract the model must follow.

The result is a clean separation of concerns:

• LangGraph still owns graph execution and persistence
• CopilotKit owns the chat-facing runtime contract
• your custom endpoint glues them together inside one deployment

Structure the frontend app

On the frontend, wrap your app in CopilotKit and point it at the custom runtime URL:

import { CopilotKit } from "@copilotkit/react-core";
import { CopilotChat, useAgentContext } from "@copilotkit/react-core/v2";
import { s } from "@hashbrownai/core";

import { useChatKit } from "@/components/chat/chat-kit";
import { chatTheme } from "@/lib/chat-theme";

export function App() {
  return (
    <CopilotKit runtimeUrl={import.meta.env.VITE_RUNTIME_URL ?? "/api/copilotkit"}>
      <Page />
    </CopilotKit>
  );
}

function Page() {
  const chatKit = useChatKit();

  useAgentContext({
    description: "output_schema",
    value: s.toJsonSchema(chatKit.schema),
  });

  return <CopilotChat {...chatTheme} />;
}

There are two important pieces here:

• runtimeUrl="/api/copilotkit" sends the chat to your custom backend route rather than directly to the raw LangGraph API
• useAgentContext(...) sends the UI schema to the agent so the model knows what structured output format it should produce

Register the dynamic components

The component registry lives in useChatKit(). This is where you define the set of components the agent is allowed to emit, such as cards, rows, columns, charts, code blocks, and buttons.

import { s } from "@hashbrownai/core";
import { exposeComponent, exposeMarkdown, useUiKit } from "@hashbrownai/react";

import { Button } from "@/components/ui/button";
import { Card } from "@/components/ui/card";
import { CodeBlock } from "@/components/ui/code-block";
import { Row, Column } from "@/components/ui/layout";
import { SimpleChart } from "@/components/ui/simple-chart";

export function useChatKit() {
  return useUiKit({
    components: [
      exposeMarkdown(),
      exposeComponent(Card, {
        name: "card",
        description: "Card to wrap generative UI content.",
        children: "any",
      }),
      exposeComponent(Row, {
        name: "row",
        props: {
          gap: s.string("Tailwind gap size") as never,
        },
        children: "any",
      }),
      exposeComponent(Column, {
        name: "column",
        children: "any",
      }),
      exposeComponent(SimpleChart, {
        name: "chart",
        props: {
          labels: s.array("Category labels", s.string("A label")),
          values: s.array("Numeric values", s.number("A value")),
        },
        children: false,
      }),
      exposeComponent(CodeBlock, {
        name: "code_block",
        props: {
          code: s.streaming.string("The code to display"),
          language: s.string("Programming language") as never,
        },
        children: false,
      }),
      exposeComponent(Button, {
        name: "button",
        children: "text",
      }),
    ],
  });
}

This registry becomes the contract between the agent and the UI. The model is not generating arbitrary JSX. It is generating structured data that must validate against the components and props you exposed.

Render assistant messages as dynamic UI

Once the assistant response arrives, the custom message renderer decides how to display it. In this example:

• assistant messages are parsed as structured JSON against the UI kit schema
• valid structured output is rendered as real React components
• user messages are rendered as ordinary chat bubbles

import type { AssistantMessage } from "@ag-ui/core";
import type { RenderMessageProps } from "@copilotkit/react-ui";
import { useJsonParser } from "@hashbrownai/react";
import { memo } from "react";

import { useChatKit } from "@/components/chat/chat-kit";
import { Squircle } from "@/components/squircle";

const AssistantMessageRenderer = memo(function AssistantMessageRenderer({
  message,
}: {
  message: AssistantMessage;
}) {
  const kit = useChatKit();
  const { value } = useJsonParser(message.content ?? "", kit.schema);

  if (!value) return null;

  return (
    <div className="group/msg mt-2 flex w-full justify-start">
      <div className="magic-text-output w-full px-1 py-1">{kit.render(value)}</div>
    </div>
  );
});

export function CustomMessageRenderer({ message }: RenderMessageProps) {
  if (message.role === "assistant") {
    return <AssistantMessageRenderer message={message} />;
  }

  return (
    <div className="flex w-full justify-end">
      <Squircle className="w-full max-w-[64ch] px-4 py-3">
        <pre>{typeof message.content === "string" ? message.content : JSON.stringify(message.content, null, 2)}</pre>
      </Squircle>
    </div>
  );
}

This renderer pattern is what makes the integration feel native:

• CopilotKit handles chat state and transport
• the custom renderer decides how assistant payloads become UI
• Hashbrown turns validated structured data into concrete React elements

Best practices

• Keep the custom endpoint thin: use it to adapt CopilotKit to your graph deployment, not to duplicate business logic already inside the graph
• Send the schema explicitly: useAgentContext should describe the UI contract every time the page mounts
• Register a constrained component set: expose only the components and props you actually want the model to use
• Treat rendering as a parsing step: parse assistant content against your schema before rendering it
• Keep user messages plain: only assistant messages need the structured renderer; user messages can stay normal chat bubbles

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