Use this skill when working with A2UI (Agent-to-User Interface) - Google's open protocol for agent-driven declarative UIs. Triggers on tasks involving A2UI message generation, component catalogs, data binding, surface management, renderer development, custom components, or integrating A2UI with A2A Protocol, AG UI, or agent frameworks like Google ADK. Covers building agents that generate A2UI JSON, setting up client renderers (Lit, React, Angular, Flutter), creating custom catalogs, and handling client-to-server actions.
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Use this skill when working with A2UI (Agent-to-User Interface) - Google's open protocol for agent-driven declarative UIs. Triggers on tasks involving A2UI message generation, component catalogs, data binding, surface management, renderer development, custom components, or integrating A2UI with A2A Protocol, AG UI, or agent frameworks like Google ADK. Covers building agents that generate A2UI JSON, setting up client renderers (Lit, React, Angular, Flutter), creating custom catalogs, and handling client-to-server actions.
[{"url":"https://github.com/google/A2UI","accessed":"2026-03-14T00:00:00.000Z","description":"Official GitHub repository with specification, renderers, and samples"},{"url":"https://a2ui.org/","accessed":"2026-03-14T00:00:00.000Z","description":"Official project site with documentation"}]
license
MIT
maintainers
[{"github":"maddhruv"}]
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A2UI - Agent-to-User Interface Protocol
A2UI is an open-source protocol from Google that enables AI agents to generate
rich, interactive user interfaces through declarative JSON rather than executable
code. It solves the critical challenge of safely transmitting UI across trust
boundaries in multi-agent systems - agents describe UI intent using a flat list
of pre-approved components, and clients render them natively across web, mobile,
and desktop. The format is optimized for LLM generation with streaming support,
incremental updates, and framework-agnostic rendering.
When to use this skill
Trigger this skill when the user:
Wants to build an agent that generates A2UI JSON responses
Needs to set up a client renderer (Lit, React, Angular, Flutter) for A2UI
Is working with A2UI message types (surfaceUpdate, createSurface, etc.)
Wants to create or customize an A2UI component catalog
Needs to implement data binding between components and a data model
Is integrating A2UI with A2A Protocol or AG UI transport
Wants to handle client-to-server actions (button clicks, form submissions)
Is building custom components or extending the basic catalog
Do NOT trigger this skill for:
General UI framework questions unrelated to agent-generated interfaces
A2A Protocol questions that don't involve UI rendering
git clone https://github.com/google/a2ui.git
cd a2ui
export GEMINI_API_KEY="your_key"cd samples/client/lit
npm install
npm run demo:all
Core concepts
Adjacency list model: A2UI uses a flat list of components with ID references
instead of nested trees. This is easier for LLMs to generate incrementally and
enables progressive rendering. Each component has an id, type, and
properties.
Surfaces: A surface is a UI container identified by surfaceId. Components
and data models are scoped to surfaces. Multiple surfaces can exist independently.
A surface is locked to a catalog for its lifetime.
Data binding: Components connect to application state via JSON Pointer paths
(RFC 6901). The data model is separate from UI structure, enabling reactive
updates. Input components (TextField, CheckBox) bind bidirectionally.
Catalogs: JSON Schema files defining which components, functions, and themes
an agent can use. The Basic Catalog provides standard components. Production apps
define custom catalogs matching their design system. Agents can only request
pre-approved components from the negotiated catalog.
createSurface/updateComponents/updateDataModel, flat component syntax, direct strings, required catalogId
Common tasks
Generate a v0.9 A2UI surface with components
Create a surface, add components, set data, in JSONL format (one JSON per line):
{"version":"v0.9","createSurface":{"surfaceId":"main","catalogId":"https://a2ui.org/specification/v0_9/basic_catalog.json"}}{"version":"v0.9","updateComponents":{"surfaceId":"main","components":[{"id":"header","component":"Text","text":"Book Your Table","variant":"h1"},{"id":"date-input","component":"DateTimeInput","label":"Select Date","value":{"path":"/reservation/date"},"enableDate":true},{"id":"submit-btn","component":"Button","child":"btn-text","variant":"primary","action":{"event":{"name":"confirm_booking"}}}]}}{"version":"v0.9","updateDataModel":{"surfaceId":"main","path":"/reservation","value":{"date":"2025-12-15","time":"19:00","guests":2}}}
Generate a v0.8 A2UI surface (legacy)
{"surfaceUpdate":{"surfaceId":"main","components":[{"id":"header","component":{"Text":{"text":{"literalString":"Book Your Table"},"usageHint":"h1"}}},{"id":"date-picker","component":{"DateTimeInput":{"label":{"literalString":"Select Date"},"value":{"path":"/reservation/date"},"enableDate":true}}},{"id":"submit-btn","component":{"Button":{"child":"submit-text","action":{"name":"confirm_booking"}}}}]}}{"dataModelUpdate":{"surfaceId":"main","contents":[{"key":"reservation","valueMap":[{"key":"date","valueString":"2025-12-15"},{"key":"time","valueString":"19:00"},{"key":"guests","valueInt":2}]}]}}{"beginRendering":{"surfaceId":"main","root":"header"}}
v0.8 requires beginRendering before the client renders. v0.9 renders on createSurface.
Handle client-to-server actions
Wire a button to dispatch an event with context from the data model:
Add validation checks that auto-disable the button:
{"checks":[{"condition":{"call":"required","args":{"value":{"path":"/partySize"}}},"message":"Party size is required"}]}
Build an agent with Google ADK
from google.adk import Agent
import json
import jsonschema
# Load A2UI schema for validationwithopen("a2ui_schema.json") as f:
a2ui_schema = json.load(f)
AGENT_INSTRUCTION = """You are a restaurant booking agent.
When the user wants to book, generate A2UI JSON after the delimiter ---a2ui_JSON---
Output a JSON list of A2UI messages using the v0.9 format."""
agent = Agent(
model="gemini-2.5-flash",
name="booking_agent",
instruction=AGENT_INSTRUCTION,
)
# Validate generated A2UI before sendingdefvalidate_a2ui(json_string):
parsed = json.loads(json_string)
jsonschema.validate(instance=parsed, schema=a2ui_schema)
return parsed
Use data binding with dynamic lists
Render a list of items from the data model using templates:
Check component type exists in catalog and all required properties are set
Unknown component type
Agent used a component not in the negotiated catalog
Verify agent prompt includes correct catalog; add component to custom catalog
Data binding resolution failure
JSON Pointer path doesn't exist in data model
Send updateDataModel before referencing the path; check for typos in path
Surface not found
Operating on a surfaceId that hasn't been created
Send createSurface (v0.9) or surfaceUpdate (v0.8) first
Catalog negotiation failure
No matching catalog between agent and client
Include supportedCatalogIds in client metadata; check agent's advertised catalogs
Gotchas
v0.8 vs v0.9 syntax is incompatible - The two spec versions use entirely different message shapes (surfaceUpdate vs createSurface, nested component syntax vs flat). Mixing them in the same stream will fail silently on most renderers. Confirm the renderer version before generating any output.
beginRendering is mandatory in v0.8 - In v0.8, the client will not render anything until it receives a beginRendering message with the root component ID. Forgetting it causes a blank surface with no error. In v0.9, createSurface triggers rendering immediately.
Catalog lock-in for the surface lifetime - Once a surface is created with a catalogId, it cannot be changed. If you reference a component from a different catalog, it will fail validation. Plan the catalog choice before streaming any messages.
JSON Pointer paths must pre-exist in the data model - A data binding like {"path": "/reservation/date"} will fail to resolve if the data model hasn't been populated yet. Always send updateDataModel (v0.9) or dataModelUpdate (v0.8) before referencing any path.
Adjacency list child references must be IDs, not inline objects - Components reference children by string ID only. Embedding a child component object inline instead of by ID will fail schema validation without a useful error message.
References
For detailed content on specific sub-domains, read the relevant file
from the references/ folder:
references/components.md - full component reference with all types and properties
references/messages.md - complete message format for v0.8 and v0.9
references/catalogs-and-actions.md - catalog schema, negotiation, and client-to-server actions
references/renderer-guide.md - implementation checklist for building custom renderers
Only load a references file if the current task requires it - they are
long and will consume context.
Companion check
On first activation of this skill in a conversation: check which companion skills are installed by running ls ~/.claude/skills/ ~/.agent/skills/ ~/.agents/skills/ .claude/skills/ .agent/skills/ .agents/skills/ 2>/dev/null. Compare the results against the recommended_skills field in this file's frontmatter. For any that are missing, mention them once and offer to install:
