The Jetpack Compose A2UI renderer defines a layered architecture that lets you choose the right layer to build on. In addition to semantic layering, a clear naming scheme communicates API intent and controls visibility to avoid polluting your classpath with unnecessary internal types.

APIs are organized into two primary categories based on use case and visibility:

1. APIs for app and component developers: Public APIs intended for direct use have clean, concise names with the A2ui prefix (or design-system and testing prefixes such as MaterialA2ui and A2uiTest). Examples include A2uiCatalog, A2uiComponent, and A2uiException.
2. APIs for UI framework integrators: APIs used by libraries bridging the core data layer and UI frameworks have descriptive names prefixed with A2uiCore. These APIs aren't intended for direct application reference and remain hidden from standard application code. Examples include A2uiCoreCatalog, A2uiCoreDataModel, and A2uiCoreSurfaceModel.

Because the core data layer contains types from both categories, it's distributed across two separate artifacts: androidx.a2ui:a2ui-model (for app developers) and androidx.a2ui:a2ui-engine (for framework integrators). This structure allows framework libraries to depend on a2ui-engine as an implementation dependency, preventing A2uiCore types from polluting public app classpaths.

Category 1: App developer APIs

The following tables list public APIs intended for application and component developers.

androidx.a2ui:a2ui-model

Type	Description
A2uiSurfaceModel	Read-only interface representing a UI surface
A2uiMessageProcessor	Entry-point type for processing incoming messages
A2uiMessageParser	Parser interface for protocol messages
A2uiServerToClientMessage	Incoming message payload
A2uiSchema	Types used to define component property schemas
A2uiException	Exceptions thrown and handled across layers
A2uiUserAction	Action payload created as a result of user interactions
A2uiClientToServerMessage	Base type for all outbound message payloads
A2uiActionInterceptor	Data-layer-level user action interceptor
A2uiFunctionDefinition	Definition of a local client function
A2uiDataPath	JSON pointer path representation

androidx.a2ui.compose:compose-runtime

Type	Description
a2uiRuntimeMessageProcessor	Extension constructor for the message processor
A2uiMessageParser	Extension constructor for the message parser
A2uiComponentState	Interface representing reactive component state
A2uiComponentModel	Data model for a successfully resolved component
A2uiComponentProperties	Stable property container optimizing recompositions
A2uiProperty	Strongly typed component property definition
A2uiComponentScope	Receiver scope for evaluating bindings and child components
A2uiComponentReference	Pointer for resolving nested child components

androidx.a2ui.compose:compose-ui

Type	Description
A2uiCatalog	Interface and extension constructor for defining catalogs
A2uiComponent	Interface for defining Compose component implementations
A2uiComponent (composable)	Composable function that emits UI for a component

androidx.compose.material3:material3-a2ui

Type	Description
A2uiSurface	Composable entry point that renders a surface
materialA2uiBasicCatalogV1	Factory function for creating an instance of the Basic Catalog that uses Material 3 components
MaterialA2uiBasicCatalogV1Defaults	Default Material 3 implementations of the Basic Catalog

androidx.a2ui.compose:compose-ui-testing

Type	Description
A2uiTestController	Test controller for orchestrating test execution
A2uiComponentStub	Stubbed or overridden component implementation
A2uiTestSurface	Composable function that renders a test surface

Category 2: Framework integrator APIs

The following table lists APIs intended for framework integrators.

androidx.a2ui:a2ui-engine

Type	Description
A2uiCoreCatalog	Contains a set of A2uiCoreComponentDefinition objects
A2uiCoreCatalogSerializer	Serializer for A2UI catalogs
A2uiCoreComponentDefinition	Contains metadata defining a component
A2uiCoreSurfaceModel	Implements A2uiSurfaceModel, exposes registries
A2uiCoreSurfaceGroupModel	Implements A2uiSurfaceGroupModel
A2uiCoreMessageProcessor	Implements A2uiMessageProcessor
A2uiCoreDataModel	Reactive data model holder
A2uiCoreComponentRegistry	Component registry
A2uiCoreValueResolver	Data accessor for use in the dynamic evaluator
A2uiCoreSchemaValidator	Component schema validator