Chat UI

Chat UI SDK

@openbench/chat-ui is a standalone React component library for rendering interactive chat interfaces powered by A2UI v0.10 JSONL (Google's declarative JSON streaming UI protocol).

A2UI v0.10 Key Points

• 4 message types: createSurface, updateComponents, updateDataModel, deleteSurface
• Every message has "version": "v0.10"
• Components are flat objects: {id, component, ...properties} (NOT nested)
• Root component must have id: "root"
• Data binding via JSON Pointer (RFC 6901): {"path": "/user/name"}
• Actions: {event: {name, context}} or {functionCall: {call, args}}
• 14 standard functions for validation and formatting
• checks system for input validation

AG-UI Streaming Events

The frontend receives AG-UI events via SSE, including progressive text streaming:

The useChat hook handles all events automatically. Text appears progressively via TEXT_MESSAGE_CONTENT deltas, then rich content (charts, files) renders via A2UI CUSTOM events.

Package Location

packages/chat-ui/
├── src/
│   ├── index.ts              # Public API exports
│   ├── types.ts              # All TypeScript interfaces
│   ├── core/                 # No React dependency
│   │   ├── transport.ts      # SSE + REST client
│   │   ├── message-processor.ts  # A2UI v0.10 JSONL parser
│   │   ├── chat-store.ts     # Zustand store
│   │   └── utils.ts          # Helpers
│   ├── a2ui/                 # A2UI rendering
│   │   ├── surface-renderer.tsx
│   │   ├── catalog.ts        # Component registry
│   │   ├── data-binding.ts   # JSON Pointer resolver + function evaluator
│   │   ├── standard/         # 18 standard A2UI components
│   │   └── custom/           # 6 OpenBench extensions
│   ├── components/           # Pre-built chat UI
│   └── hooks/                # React hooks
├── styles/
│   └── chat-ui.css           # Default styles
└── tests/

Usage Patterns

Drop-in (full chat page)

import { ChatProvider, ChatPanel, SessionSidebar } from '@openbench/chat-ui';
import '@openbench/chat-ui/styles/chat-ui.css';

function ChatPage() {
  return (
    <ChatProvider config={{ streamUrl: '/awp' }}>
      <div className="flex h-screen">
        <SessionSidebar />
        <ChatPanel className="flex-1" />
      </div>
    </ChatProvider>
  );
}

Custom UI with hooks

import { useChat } from '@openbench/chat-ui';

function MyChat() {
  const { messages, sendMessage, isStreaming } = useChat({
    streamUrl: '/awp',
  });
  return (
    <div>
      {messages.map(m => <div key={m.id}>{m.content}</div>)}
      <button => sendMessage('Hello!')}>Send</button>
    </div>
  );
}

Extend A2UI catalog

import { registerCustomComponent } from '@openbench/chat-ui';
registerCustomComponent('MyWidget', MyWidgetComponent);

A2UI Component Catalog

Standard (18 from A2UI v0.10)

Text, Image, Icon, Video, AudioPlayer, Row, Column, List, Card, Tabs, Modal, Divider, Button, TextField, CheckBox, ChoicePicker, Slider, DateTimeInput

Custom (6 OpenBench extensions)

Note: AudioPlayer and Video are standard A2UI components -- no custom wrappers needed.

Standard Functions (14)

Validation: required, regex, length, numeric, email Formatting: formatString, formatNumber, formatCurrency, formatDate, pluralize Navigation: openUrl Logic: and, or, not

SurfaceRenderer

Converts A2UI v0.10 adjacency list to React component tree:

import { SurfaceRenderer } from '@openbench/chat-ui';

<SurfaceRenderer
  surface={a2uiSurface}
  => transport.send(action)}
/>

Processing:

1. Index components by ID in Map
2. Find component with id: "root"
3. Look up component type in catalog -> React component
4. Resolve Dynamic* properties (literal | DataBinding | FunctionCall)
5. Resolve ChildList (array of IDs or template with data path)
6. Recursively render children
7. Wire action handlers (resolve context, dispatch A2UIAction)
8. Handle two-way binding for input components

Design System

Notion-inspired, monochrome, icon-driven. No emojis.

• Colors: Carbon (#1a1a1a) on White (#ffffff), Gray scale for hierarchy
• Icons: Lucide React (clean, consistent, 1px stroke)
• Typography: System font stack (Inter where available)
• Borders: 1px solid rgba(0,0,0,0.08) -- subtle, not heavy shadows
• Spacing: 4px base unit, consistent padding/margin multiples

See docs/DESIGN_SYSTEM.md for full design tokens.

Build Commands

cd packages/chat-ui
pnpm install          # Install dependencies
pnpm dev              # Dev server
pnpm build            # Build library (ESM + .d.ts)
pnpm tsc --noEmit     # Type check
pnpm vitest           # Run tests

Anti-Patterns

DO NOT:

• Import from internal paths -- use public API from @openbench/chat-ui
• Use emojis in the UI -- use Lucide icons exclusively
• Add heavy shadows or gradients -- keep Notion-like flat, subtle aesthetic
• Skip data-binding resolution -- always resolve JSON Pointers before rendering
• Create A2UI components without registering in catalog -- use registerCustomComponent()
• Mix CSS-in-JS with plain CSS -- use plain CSS with CSS custom properties
• Use "type" on components -- the correct A2UI field is "component"
• Nest properties inside a "properties" dict -- A2UI properties are flat
• Use invented message types like surfaceUpdate or beginRendering
• Forget to implement standard functions in the data-binding evaluator

Cross-References

• Chat Layer: Python backend that produces A2UI v0.10 JSONL -> see chat-layer skill
• Composing Workflows: ChatLayer L2 composition -> see composing-workflows skill
• Testing: Component and hook tests -> see testing-openbench skill

For architecture details, see docs/CHAT_UI_ARCHITECTURE.md For design tokens, see docs/DESIGN_SYSTEM.md

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