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gen ui demo

2026 · live · 2-day prototype · solo

Two Claude tool-use calls in series. Stage 1 picks components from a tiny web-component library and fills them with content. Stage 2 arranges them into a layout. The renderer is plain Svelte. The LLM never writes code.

try it

Pick a starter prompt or write your own. Currently running on mocks — full Anthropic wiring lands next.

how it works

Stage 1 — content + component selection

Anthropic Messages API call with a tool schema describing each component (name, description, prop types). The model returns its choices as tool_use blocks. The app parses them into a flat array of { component, props } pairs. The model never returns JSX, HTML, or CSS.

Stage 2 — layout decision

Second Messages API call. The component array from Stage 1 is the input. The tool schema defines a recursive grid layout (type, columns, children, span). Output is a single layout object referencing components by index.

Stage 3 — deterministic render

A recursive Svelte component walks the layout JSON and renders each web component with its filled props. Plain application code. No LLM involvement. Predictable, testable, debuggable.

what this proved

• The composition / rendering split holds. The LLM reasons about which components and what content; the application code draws. Each side is good at its job.
• Tool schemas are the contract. Constraining all model output to typed JSON eliminates the code-correctness and injection risks that block production use of free-form LLM output.
• A well-designed design system is the substrate. Framework-agnostic web components with constrained props were the right shape for this years before generative UI was a real category. The original prototype validated AXS’s architecture as durable against the GenAI paradigm shift.

stack

Frontend

Astro, Svelte 5, Lit web components

Pipeline

Anthropic Messages API, two-stage tool use, async generator stream

Hosting

Cloudflare Pages + Pages Functions

Original prototype

Svelte, Node.js, AWS Bedrock with Claude tool use

Full write-up: Generating UI Without Generating Code · source on github