A2UI Atomic Catalog
The A2UI Atomic Catalog is an open-source, typed UI vocabulary — 474 atoms —
that AI agents use to produce real rendered interfaces instead of generating HTML. An agent
names a component (stat_card, gauge_sla, stepper) and
passes data; a renderer that already knows that component draws it.
A model writing HTML has to be correct every time, and its failure mode is markup that is subtly wrong in ways nobody notices. A model naming a component from a fixed set can only fail by naming something that does not exist — which fails immediately, at the schema boundary. Constraining the output makes the system more reliable, not less capable.
The same payload renders on the web, Google Meet stages, Apps Script web apps, Google Chat cards, and MCP Apps hosts such as claude.ai. Per-surface support is declared per atom, so an atom that cannot work somewhere says so rather than degrading silently.
This is an independent, unofficial project. It is not affiliated with, endorsed by, or sponsored by Google or Anthropic. A2UI is Google's protocol (official spec at a2ui.org); MCP is Anthropic's. The catalogue is MIT licensed and the full source is on GitHub.
Built and maintained by Curtis Krygier. Design notes and build write-ups are published on the blog.