---

name: building-chat-interfaces description: | Build AI chat interfaces with custom backends, authentication, and context injection. Use when integrating chat UI with AI agents, adding auth to chat, injecting user/page context, or implementing httpOnly cookie proxies. Covers ChatKitServer, useChatKit, and MCP auth patterns. NOT when building simple chatbots without persistence or custom agent integration.

Building Chat Interfaces

Build production-grade AI chat interfaces with custom backend integration.

Quick Start

# Backend (Python)
uv add chatkit-sdk agents httpx

# Frontend (React)
npm install @openai/chatkit-react

---

Core Architecture

Frontend (React)                    Backend (Python)
┌─────────────────┐                ┌─────────────────┐
│  useChatKit()   │───HTTP/SSE───>│  ChatKitServer  │
│  - custom fetch │                │  - respond()    │
│  - auth headers │                │  - store        │
│  - page context │                │  - agent        │
└─────────────────┘                └─────────────────┘

---

Backend Patterns

1. ChatKit Server with Custom Agent

from chatkit.server import ChatKitServer
from chatkit.agents import stream_agent_response
from agents import Agent, Runner

class CustomChatKitServer(ChatKitServer[RequestContext]):
    """Extend ChatKit server with custom agent."""

    async def respond(
        self,
        thread: ThreadMetadata,
        input_user_message: UserMessageItem | None,
        context: RequestContext,
    ) -> AsyncIterator[ThreadStreamEvent]:
        if not input_user_message:
            return

        # Load conversation history
        previous_items = await self.store.load_thread_items(
            thread.id, after=None, limit=10, order="desc", context=context
        )

        # Build history string for prompt
        history_str = "\n".join([
            f"{item.role}: {item.content}"
            for item in reversed(previous_items.data)
        ])

        # Extract context from metadata
        user_info = context.metadata.get('userInfo', {})
        page_context = context.metadata.get('pageContext', {})

        # Create agent with context in instructions
        agent = Agent(
            name="Assistant",
            tools=[your_search_tool],
            instructions=f"{history_str}\nUser: {user_info.get('name')}\n{system_prompt}",
        )

        # Run agent with streaming
        result = Runner.run_streamed(agent, input_user_message.content)
        async for event in stream_agent_response(context, result):
            yield event

2. Database Persistence

from sqlmodel.ext.asyncio.session import AsyncSession
from sqlalchemy.ext.asyncio import create_async_engine

DATABASE_URL = os.getenv("DATABASE_URL").replace("postgresql://", "postgresql+asyncpg://")
engine = create_async_engine(DATABASE_URL, pool_pre_ping=True)

# Pre-warm connections on startup
async def warmup_pool():
    async with engine.begin() as conn:
        await conn.execute(text("SELECT 1"))

3. JWT/JWKS Authentication

from jose import jwt
import httpx

async def get_current_user(authorization: str = Header()):
    token = authorization.replace("Bearer ", "")
    async with httpx.AsyncClient() as client:
        jwks = (await client.get(JWKS_URL)).json()
    payload = jwt.decode(token, jwks, algorithms=["RS256"])
    return payload

---

Frontend Patterns

1. Custom Fetch Interceptor

const { control, sendUserMessage } = useChatKit({
  api: {
    url: `${backendUrl}/chatkit`,
    domainKey: domainKey,

    // Custom fetch to inject auth and context
    fetch: async (url: string, options: RequestInit) => {
      if (!isLoggedIn) {
        throw new Error('User must be logged in');
      }

      const pageContext = getPageContext();
      const userInfo = { id: userId, name: user.name };

      // Inject metadata into request body
      let modifiedOptions = { ...options };
      if (modifiedOptions.body && typeof modifiedOptions.body === 'string') {
        const parsed = JSON.parse(modifiedOptions.body);
        if (parsed.params?.input) {
          parsed.params.input.metadata = {
            userId, userInfo, pageContext,
            ...parsed.params.input.metadata,
          };
          modifiedOptions.body = JSON.stringify(parsed);
        }
      }

      return fetch(url, {
        ...modifiedOptions,
        headers: {
          ...modifiedOptions.headers,
          'X-User-ID': userId,
          'Content-Type': 'application/json',
        },
      });
    },
  },
});

2. Page Context Extraction

const getPageContext = useCallback(() => {
  if (typeof window === 'undefined') return null;

  const metaDescription = document.querySelector('meta[name="description"]')
    ?.getAttribute('content') || '';

  const mainContent = document.querySelector('article') ||
                     document.querySelector('main') ||
                     document.body;

  const headings = Array.from(mainContent.querySelectorAll('h1, h2, h3'))
    .slice(0, 5)
    .map(h => h.textContent?.trim())
    .filter(Boolean)
    .join(', ');

  return {
    url: window.location.href,
    title: document.title,
    path: window.location.pathname,
    description: metaDescription,
    headings: headings,
  };
}, []);

3. Script Loading Detection

const [scriptStatus, setScriptStatus] = useState<'pending' | 'ready' | 'error'>(
  isBrowser && window.customElements?.get('openai-chatkit') ? 'ready' : 'pending'
);

useEffect(() => {
  if (!isBrowser || scriptStatus !== 'pending') return;

  if (window.customElements?.get('openai-chatkit')) {
    setScriptStatus('ready');
    return;
  }

  customElements.whenDefined('openai-chatkit').then(() => {
    setScriptStatus('ready');
  });
}, []);

// Only render when ready
{isOpen && scriptStatus === 'ready' && <ChatKit control={control} />}

---

Next.js Integration

httpOnly Cookie Proxy

When auth tokens are in httpOnly cookies (can't be read by JavaScript):

// app/api/chatkit/route.ts
import { NextRequest, NextResponse } from "next/server";
import { cookies } from "next/headers";

export async function POST(request: NextRequest) {
  const cookieStore = await cookies();
  const idToken = cookieStore.get("auth_token")?.value;

  if (!idToken) {
    return NextResponse.json({ error: "Not authenticated" }, { status: 401 });
  }

  const response = await fetch(`${API_BASE}/chatkit`, {
    method: "POST",
    headers: {
      Authorization: `Bearer ${idToken}`,
      "Content-Type": "application/json",
    },
    body: await request.text(),
  });

  // Handle SSE streaming
  if (response.headers.get("content-type")?.includes("text/event-stream")) {
    return new Response(response.body, {
      status: response.status,
      headers: {
        "Content-Type": "text/event-stream",
        "Cache-Control": "no-cache",
      },
    });
  }

  return NextResponse.json(await response.json(), { status: response.status });
}

Script Loading Strategy

// app/layout.tsx
import Script from "next/script";

export default function RootLayout({ children }: { children: React.ReactNode }) {
  return (
    <html lang="en">
      <head>
        {/* MUST be beforeInteractive for web components */}
        <Script
          src="https://cdn.platform.openai.com/deployments/chatkit/chatkit.js"
          strategy="beforeInteractive"
        />
      </head>
      <body>{children}</body>
    </html>
  );
}

---

MCP Tool Authentication

MCP protocol doesn't forward auth headers. Pass credentials via system prompt:

SYSTEM_PROMPT = """You are Assistant.

## Authentication Context
- User ID: {user_id}
- Access Token: {access_token}

CRITICAL: When calling ANY MCP tool, include:
- user_id: "{user_id}"
- access_token: "{access_token}"
"""

# Format with credentials
instructions = SYSTEM_PROMPT.format(
    user_id=context.user_id,
    access_token=context.metadata.get("access_token", ""),
)

---

Common Pitfalls

Issue	Symptom	Fix
History not in prompt	Agent doesn't remember conversation	Include history as string in system prompt
Context not transmitted	Agent missing user/page info	Add to request metadata, extract in backend
Script not loaded	Component fails to render	Detect script loading, wait before rendering
Auth headers missing	Backend rejects requests	Use custom fetch interceptor
httpOnly cookies	Can't read token from JS	Create server-side API route proxy
First request slow	7+ second delay	Pre-warm database connection pool

---

Verification

Run: python3 scripts/verify.py

Expected: ✓ building-chat-interfaces skill ready

If Verification Fails

1. Check: references/ folder has chatkit-integration-patterns.md
2. Stop and report if still failing

Related Skills (Tiered System)

• streaming-llm-responses - Tier 2: Response lifecycle, progress updates, client effects
• building-chat-widgets - Tier 3: Interactive widgets, entity tagging, composer tools
• fetching-library-docs - ChatKit docs: --library-id /openai/chatkit --topic useChatKit

References

• references/chatkit-integration-patterns.md - Complete patterns with evidence
• references/nextjs-httponly-proxy.md - Next.js cookie proxy patterns