Claude.ai's generative UI - reverse-engineered, rebuilt for pi.

Ask pi to "show me how compound interest works" and get a live interactive widget - sliders, charts, animations - rendered in a native macOS window. Not a screenshot. Not a code block. A real HTML application with JavaScript, streaming live as the LLM generates it.

On claude.ai, when you ask Claude to visualize something, it calls a tool called show_widget that renders HTML inline in the conversation. The HTML streams live - you see cards, charts, and sliders appear as tokens arrive.

This extension replicates that system for pi:

1. LLM calls visualize_read_me - loads design guidelines (lazy, only the relevant modules)
2. LLM calls show_widget - generates an HTML fragment as a tool call parameter
3. Extension intercepts the stream - opens a native macOS window via Glimpse and feeds partial HTML as tokens arrive
4. morphdom diffs the DOM - new elements fade in smoothly, unchanged elements stay untouched
5. Scripts execute on completion - Chart.js, D3, Three.js, anything from CDN

The widget window has full browser capabilities (WKWebView) and a bidirectional bridge - window.glimpse.send(data) sends data back to the agent.

pi install git:github.com/user/pi-generative-ui

macOS only. Requires Swift toolchain (ships with Xcode or Xcode Command Line Tools).

Just ask pi to visualize things. The extension adds two tools that the LLM calls automatically:

• "Show me how compound interest works" → interactive explainer with sliders and Chart.js
• "Visualize the architecture of a transformer" → SVG diagram with labeled components
• "Create a dashboard for this data" → metric cards, charts, tables
• "Draw a particle system" → Canvas animation

The LLM decides when to use widgets vs text based on the request. Explanatory/visual requests trigger widgets; code/text requests stay in the terminal.

The design guidelines aren't hand-written. They're extracted verbatim from claude.ai.

Here's the trick: you can export any claude.ai conversation as JSON. The export includes full tool call payloads - including the complete read_me tool results containing Anthropic's actual design system. 72K of production rules covering typography, color palettes, streaming-safe CSS patterns, Chart.js configuration, SVG diagram engineering, and more.

We triggered read_me with each module combination, exported the conversation, parsed the JSON, split the responses into deduplicated sections, and verified byte-level accuracy against the originals. The result: our LLM gets the exact same instructions Claude gets on claude.ai.

Five modules, loaded on demand:

The extension intercepts pi's streaming events (toolcall_start / toolcall_delta / toolcall_end) to render the widget live as tokens arrive:

toolcall_start    → initialize streaming state
toolcall_delta    → debounce 150ms, open window, morphdom diff
toolcall_end      → final diff + execute <script> tags
execute()         → reuse window, wait for interaction or close

Key details:

• Shell HTML + JS eval - window opens with an empty shell; content injected via win.send(), not setHTML(), to avoid full-page flashes
• morphdom DOM diffing - only changed nodes update; new nodes get a 0.3s fade-in animation
• pi-ai's parseStreamingJson - no need for a partial JSON parser; pi already provides parsed arguments on every delta
• 150ms debounce - batches rapid token updates for smooth visual rendering
• Dark mode by default - #1a1a1a background, designed for macOS WKWebView

Glimpse is a native macOS micro-UI library. It opens a WKWebView window in under 50ms via a tiny Swift binary. No Electron, no browser tab, no runtime dependencies beyond the system WebKit.

The Swift source compiles automatically on npm install via postinstall.

pi-generative-ui/
├── .pi/extensions/generative-ui/
│   ├── index.ts              # Extension: tools, streaming, Glimpse integration
│   ├── guidelines.ts         # 72K of verbatim claude.ai design guidelines
│   └── claude-guidelines/    # Raw extracted markdown (reference)
│       ├── art.md
│       ├── chart.md
│       ├── diagram.md
│       ├── interactive.md
│       ├── mockup.md
│       └── sections/         # Deduplicated sections
└── package.json              # pi-package manifest

1. Start a conversation on claude.ai that triggers show_widget
2. Call read_me with each module combination (art, chart, diagram, interactive, mockup)
3. Export the conversation as JSON from claude.ai settings
4. Parse the JSON - every tool_result for visualize:read_me contains the complete guidelines
5. Split each response at ## heading boundaries
6. Deduplicate shared sections (e.g., "Color palette" appears in chart, mockup, interactive, diagram)
7. Verify reconstruction matches the originals (4/5 exact, 1 has a single whitespace char difference)

The raw read_me responses are preserved in claude-guidelines/ - the original markdown exactly as claude.ai returned it, before splitting and deduplication. The conversation export JSON is not included in this repo.

• pi - the extensible coding agent that makes this possible
• Glimpse - native macOS WKWebView windows
• morphdom - DOM diffing for smooth streaming
• Anthropic - for building the generative UI system we reverse-engineered

MIT