The vocabulary layer for A2UI — useful for humans · declarative for agents.
The model names an atom. The renderer compiles the HTML, CSS, SVG, and animation.
Independent, unofficial catalog — not affiliated with or endorsed by Google. A2UI is Google's protocol; the official spec lives at a2ui.org.
The idea
Rather than asking an agent to generate custom UI every turn — expensive, fragile, unpredictable — give it a stable vocabulary of atoms and let it compose from those.
The model names an atom; the renderer expands it into the full HTML server-side, and that expansion never re-enters the model's context window — so the tokens spent describing a UI are a fraction of the tokens in the rendered result.
Work in progress. The atom vocabulary itself is stable; what it's for is still being explored. The live catalog and this repo are the vocabulary and its renderers — applying that vocabulary to new use cases (rendering a CLI's own output, for instance, in a sibling project not yet published) is ongoing, not finished.
Connect an agent
The catalog is consumable three ways, no signup for any of them — BYO by design: renders happen in your environment, your data never touches us.
| Channel | Endpoint | What an agent gets |
|---|
| MCP server | a2uicatalog.ai/mcp | Tools to browse catalogs, validate/compose payloads, emit render URLs, and render live views on MCP Apps hosts |
| ARD manifest | /.well-known/ard.json | Agentic Resource Discovery — every atom as a crawlable, typed entry |
| Machine catalog | a2uicatalog.ai/spec.json | The full schema in one fetch — types, fields, surface compatibility, degradation notes |
5-minute quickstarts: Claude (Desktop / claude.ai) · Gemini Enterprise (BYO-MCP)
As an agent skill — this repo ships a SKILL.md, so any agent using the
skills ecosystem can pick up the catalog's when-to-use guidance directly:
npx skills add a2uicatalog/a2ui@a2ui-atomic-catalog
A few atoms, live on the site — click through to a full spec + fields table for each:
Browse all 573 atoms →
Google Apps Script renderer — try it live
450+ atoms running natively in Google Apps Script. No CDN, no dependencies, no server. Paste a JSON block list, get a rendered page.
{
"title": "Hello A2UI",
"theme": "light",
"blocks": [
{ "type": "heading", "level": 1, "text": "My first A2UI page" },
{ "type": "callout", "icon": "💡", "text": "Built with 450+ atoms in Google Apps Script." },
{ "type": "chartjs_bar", "title": "Quick chart", "bar_color": "#6366f1",
"data": [{ "label": "A", "value": 80 }, { "label": "B", "value": 45 }, { "label": "C", "value": 62 }] }
]
}
What's in the GAS renderer
| Feature | Detail |
|---|
| 450+ atoms, growing | Apps Script surface — superset of the web article renderer |
| CSS-only interactions | Tabs, carousel, gallery lightbox, modals, accordions — zero JS required |
| Inline SVG charts | Bar, line, pie, donut, heatmap, punch card, sankey, cohort retention, GitHub activity grid |
| 8 form input types | text, email, select, radio, checkbox, switch, slider, date — native HTML controls |
| Animation fallbacks | 32 motion atoms degrade to readable content cards |
| No CDN | Works inside GAS sandboxed iframes with no external requests |
| Large payload support | Automatically switches to POST for schemas too large for a URL |
Deploy your own renderer (recommended)
The renderer is fully open source. Deploy your own instance — you own the URL, you own the deployment, no dependency on the catalog's demo endpoint.
git clone https://github.com/a2uicatalog/a2ui
cd a2ui/apps-script-surface/gas-schema-renderer
clasp login
clasp create --type webapp --title "My A2UI Renderer"
clasp push
clasp deploy
# → Your renderer is live at https://script.google.com/macros/s/YOUR_ID/exec
Call it with any payload from the catalog (illustrative — encode() stands in for gzip + base64url of the JSON, see scripts/make_url.py for the exact encoding):
function doGet() {
const blocks = [
{ type: "stat_card", value: "1,234", label: "Daily users", delta: "+12%", is_up: true },
{ type: "progress_bar", value: 75, label: "Q2 target" }
];
const url = "https://script.google.com/macros/s/YOUR_ID/exec";
return HtmlService.createHtmlOutput(
`<script>window.location="${url}?p=${encode(blocks)}"</script>`
);
}
The catalog's "Try it live" button uses a shared demo instance of the same renderer. For anything beyond exploration, deploy your own.
What's in this repo
| Directory | Contents |
|---|
atoms/ | Atom schema definitions (schema.yaml) |
renderers/ | Surface renderers — web_article.py is the canonical web renderer |
apps-script-surface/ | GAS renderer — atom.gs + atom files (450+ atoms, no CDN) |
components/ | Lit Web Components for the meet-stage surface |
scripts/ | Build pipeline — atom pages, spec.json, MCP bundle, README compat matrix, link/brand checks |
vendors/ | Landscape analysis of 9 UI libraries mapped to A2UI atoms |
benchmarks/ | Token comparison study (BENCHMARK.md) |
spec/ | Internal state/action contracts (gdm-v0.2, a2ui-state-v1) — the A2UI v1.0 candidate spec itself lives at a2ui.org, not vendored here |
examples/ | Playbook YAML examples |
knowledge-catalogue/ | Curriculum-to-atom pipeline — schema-validated curriculum markdown (Brevet 2026, NIST AI RMF) compiled into A2UI payloads. Separate concern from the atom vocabulary itself. |
573 atoms across 8 surfaces
Atoms declare which surfaces they support at the schema level. An agent picks an atom by name, supplies parameters, and the renderer handles the rest.
[{
"type": "stat_card",
"label": "Atoms published",
"value": "450+",
"delta": "+12 this week"
}]
Agents never write HTML. They compose from the vocabulary.
Surface compatibility
Every atom declares, at the schema level, which of the 8 surfaces it works on and where it degrades (with a note explaining the caveat). The matrix below is generated straight from public/spec.json — the same file agents consume — so this README can no longer drift from the catalog.
573 atoms · generated from public/spec.json by scripts/gen_compat_matrix.py — do not edit by hand.
| Atom | web | gas-web | gas-panel | meet | chat | mcp-apps | claude-code | android | email | pdf | slides | pptx | Source · license |
|---|
abbr_tooltip | ✅ | ✅ | — | ⚠️ | — | ✅ | — | ✅ | ⚠️ | — | — | — | a2uicatalog · MIT |
accordion_item | ✅ | ✅ | — | ✅ | — | ✅ | — | ✅ | — | — | — | — | a2uicatalog · MIT |
achievement_badge | ✅ | ✅ | — | ✅ | ⚠️ | ✅ | — | ✅ | ✅ | ✅ | — | — | a2uicatalog · MIT |
action_items | ✅ | ✅ | — | — | — | ✅ | — | ✅ | — | ✅ | ✅ | ✅ | a2uicatalog · MIT |
action_required_card | ✅ | ✅ | — | ✅ | ✅ | ✅ | — | ✅ | ⚠️ | — | — | — | a2uicatalog · MIT |
actual_vs_estimate | ✅ | ✅ | — | — | — | ✅ | — | ✅ |
✅ full support ⚠️ renders with caveats (degradation note in spec.json) — not declared for this surface — treat as unsupported
Vendor landscape
Nine UI libraries benchmarked against the A2UI atom vocabulary — gaps identified, licences checked, adaptation priority set. See vendors/LANDSCAPE.md for the full analysis.
| Tier | Libraries |
|---|
| Tier 1 — act now | AI-native patterns, Microsoft Fluent UI |
| Tier 2 — delivered | Shopify Polaris, Atlassian Design System, IBM Carbon |
| Tier 3 — monitor | Tailwind UI, Radix UI, MagicUI / Aceternity, Vercel Geist |
Using this vocabulary
- Copy
atoms/schema.yaml into your agent's system prompt or tool definition
- Teach your agent the composition pattern — pick atoms by name, supply parameters
- Parse the agent's output and render using:
- Google Apps Script — copy
atom.gs + atoms_charts.gs into any GAS project, call renderAtoms(blocks)
- Python / web — use
renderers/web_article.py (server-side, web-surface atoms)
- Meet Stage —
renderers/meet_stage.py for live presentation panels via gdm-html-panel
- Your own renderer — the spec is framework-agnostic
The renderer handles HTML, CSS, SVG, and animation. The model never touches them.
On the name
Google established the A2- prefix for agent-interface concepts and published the v0.9 spec in June 2026; this vocabulary is independently developed and interoperable with it. Not affiliated with Google.
The renderer has since moved to the v1.0 candidate spec (renderers/a2ui_v1.py, a2ui_v1_wired.py, a2ui_v1_updates.py) — conformant for the standard-mappable atoms and the blocks dialect's full envelope (createSurface, updateComponents, updateDataModel, action/function RPC). One real, flagged gap: the catalogue's own wired (stateful) dialect is richer than v1.0's flat dataModel — reactive primitives (filtering, computed values, validation, timers) have no v1.0 equivalent and travel as an explicit catalogId: a2ui-state-v1 extension. That's a property of bare v1.0 hosts that don't know the extension catalog — not of this catalogue's own renderer, which always carries a2ui-state-v1 and never degrades: full reactive fidelity on the surfaces that serve it. The degradation only exists as a fallback for a host that doesn't have the catalog at all, and it's spec-correct behavior in that case, not a violation. Not a blanket compliance claim either way — see the module docstrings for the exact scope.
Related work
License
MIT. See LICENSE for details.
Built by Curtis Krygier.
