Rendering engine for the A2UI protocol, enabling AI agents to generate dynamic user interfaces with full v0.8 widget catalog, JSON Pointer reactive data binding, and comprehensive event handling.
A Kotlin Multiplatform rendering engine for the A2UI protocol, enabling AI agents to generate dynamic user interfaces that render natively across platforms.
a2ui-4k implements the A2UI v0.9 specification natively, with transparent backwards-compatible support for v0.8 surfaces (transcoded internally to the v0.9 shape — see Deprecated Protocol Versions). The A2UI protocol is under active development.
action / error events with the v0.9 wire envelope ({"version":"v0.9", …})CheckRule evaluation backed by the function evaluatorAccessibility props (label, description) honored across input widgetsACTIVITY_SNAPSHOT / ACTIVITY_DELTA envelopes accepted on the same code path; per-surface protocol version drives outbound serializationimport com.contextable.a2ui4k.catalog.CoreCatalog
import com.contextable.a2ui4k.render.A2UISurface
@Composable
fun MyScreen(uiDefinition: UiDefinition) {
A2UISurface(
definition = uiDefinition,
catalog = CoreCatalog,
onEvent = { event ->
// Handle user interactions
}
)
}
a2ui-4k implements the A2UI specification from Google. For protocol details including message formats, component properties, and data binding, refer to the canonical specification.
If your agent can call client-side tools (AG-UI ToolExecutor, OpenAI
functions, Gemini tools, Anthropic tool_use), the library ships
A2UiRenderTool — a canonical, SDK-agnostic helper that maps one render_a2ui
tool call to createSurface + updateComponents + optional
on your . No new dependencies; the library stays
transport-free.
See skills/expose-a2ui-as-agent-tool.md for the full integration walkthrough and adapter snippets for other SDKs.
a2ui-4k is a rendering engine, not an A2A SDK. It is transport-agnostic and expects callers to plug it into an A2A (Agent-to-Agent) transport of their choice. Concretely, callers are responsible for:
For the A2A protocol layer itself (AgentExtension data structure, X-A2A-Extensions header, Message/Task/Part models, HTTP transport), use an A2A SDK such as the Google A2A Python SDK or your framework's agent library. See docs/api-reference/agent-extension.md for the full reference.
| Platform | Status |
|---|---|
| Android | Supported |
| JVM/Desktop | Supported |
| iOS | Supported |
# Run tests
./gradlew :library:allTests
# Publish to Maven Local
./gradlew :library:publishToMavenLocal
Copyright 2025 Contextable LLC
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance the License.
You may obtain a copy of the License at
http:
Unless applicable law agreed to writing, software
distributed under the License distributed an BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express implied.
See the License the specific language governing permissions
limitations under the License.
updateDataModelSurfaceStateManagerimport com.contextable.a2ui4k.agent.A2UiRenderTool
import com.contextable.a2ui4k.agent.A2UiRenderException
import com.contextable.a2ui4k.state.SurfaceStateManager
val manager = SurfaceStateManager()
val renderTool = A2UiRenderTool(manager)
// AG-UI Kotlin SDK adapter (~4 lines):
class RenderA2UiToolExecutor(private val tool: A2UiRenderTool) : ToolExecutor {
override val name = tool.name
override val description = tool.description
override val parameters = tool.parameters
override suspend fun execute(arguments: JsonObject) = try {
ToolExecutionResult.success(tool.render(arguments).toString())
} catch (e: A2UiRenderException) {
ToolExecutionResult.failure(e.message ?: "render_a2ui failed")
}
}
toolRegistry.registerTool(RenderA2UiToolExecutor(renderTool))
application/json+a2ui) and pass it to SurfaceStateManager.processMessage(...).A2UIClientCapabilities (built via a2uiBothVersionsClientCapabilities() or a sibling helper) under the "a2uiClientCapabilities" key in outbound A2A message metadata.UiEvent instances via toClientMessage(version) and wrap the returned JsonObject as an A2A message Part. For v0.9 surfaces with sendDataModel == true, also attach SurfaceStateManager.buildClientDataModel() under "a2uiClientDataModel" in metadata.Surfaced from shared tags and platforms — no rankings paid for.