A2UI Atomic Catalog
474 typed UI atoms an AI agent composes into real rendered interfaces — web, Google Meet, Apps Script, Google Chat and MCP Apps — instead of writing HTML by hand. The agent names a component from a fixed vocabulary; a renderer that already knows that component draws it.
Connect
MCP server, no auth, no signup, no API key:
https://a2uicatalog.ai/mcp
POST speaks JSON-RPC 2.0 (MCP Streamable HTTP). GET with Accept: application/json
returns a machine-readable descriptor listing every tool, current rate limits, and
documentation links.
How to use it
list_catalogs— pick the catalog slice the task actually needs. Do not load the whole 474-atom vocabulary into context for a one-chart request.get_catalog— read the real field contracts for that slice. Never guess a field name; a hallucinated field is a validation error, not a broken render.- Render, by host capability:
render_surface— MCP Apps-capable hosts (Claude.ai and others): renders inline in the conversation, no URL.preview_url— any other host: returns a shareable link (rate-limited demo renderer).make_surface_url— render against the caller's own deployed renderer instead of the shared demo one; no rate limit.
When this is the wrong tool
- The answer is better as prose than a visual.
- The host cannot display HTML or open a link.
- The task needs live data this catalog doesn't already declare a source for — this skill renders data, it does not fetch arbitrary data.
Reference
| Document | URL |
|---|---|
| OpenAPI specification | https://a2uicatalog.ai/openapi.json |
| Full atom vocabulary | https://a2uicatalog.ai/spec.json |
| Strict per-atom JSON Schema | https://a2uicatalog.ai/catalogue/atoms-json-schema.json |
| Agent overview | https://a2uicatalog.ai/llms.txt |
| A2A agent card | https://a2uicatalog.ai/.well-known/agent-card.json |
Free, MIT licensed, no signup. Independent, unofficial project — not affiliated with, endorsed by, or sponsored by Google or Anthropic. A2UI is Google's protocol; MCP is Anthropic's. Source: https://github.com/a2uicatalog/a2ui