Build this as two cooperating systems, not as a single “Compose MCP server”: a Kotlin MCP server exposes tools, resources, or prompts, while a separate Android app validates structured UI data and renders it with Jetpack Compose. This guide assumes the server runs as a remote Ktor service and the Android app receives UI state through an application-defined delivery path. MCP does not, by itself, define that path or make the Compose renderer an MCP server.
Choose the topology before choosing a transport
Keep the roles explicit. The MCP client connects to the MCP server; the Android app owns the renderer. An agent or backend may sit between them, but it should not blur the boundary between MCP messages and Android rendering state.
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- MCP server: registers the operations and data the MCP client can access.
- Application boundary: decides how the result of an operation becomes UI data available to the Android app. This may be an existing backend or another channel in your system; it is an application design choice, not something established by the renderer documentation.
- Android renderer: validates supported UI data, maps it to a known component catalog, displays it, and reports user actions to application logic.
For a local editor or CLI workflow, a server process using STDIO may be appropriate. For a separately hosted service, use a network transport supported by the intended MCP client and your deployment. Do not assume the Android device should host the server, or that an Android renderer can connect directly to an MCP server without an application-level integration.
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Choose a UI contract the app can safely render
The server should produce structured, versioned data—not executable UI code. On Android, the renderer maps data to components that the app deliberately supports. That constraint limits what a remote response can ask the app to display and keeps rendering decisions inside the application.
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Use Android’s A2UI renderer when its contract fits
Android’s A2UI renderer documents support for specification version 0.9.1 and uses a component catalog to map protocol data to native Compose UI. Its architecture separates model and engine processing, runtime, UI APIs, and catalog implementations. The documented artifact families include androidx.a2ui:a2ui-model, androidx.a2ui:a2ui-engine, androidx.a2ui.compose:compose-runtime, androidx.a2ui.compose:compose-ui, and a Material 3 basic catalog artifact.
Treat those names as a starting point, not a complete Gradle recipe: verify artifact availability, versions, and compatibility for your project before pinning dependencies. The version supported by a renderer and the version of its published artifacts are separate compatibility questions.
Keep a custom schema narrow if you do not use A2UI
A custom contract can work when the app and server need a smaller set of UI patterns, but document it as an application-owned protocol. Define supported component types, allowed properties, action identifiers, and a schema version. Reject unknown or malformed data predictably; do not interpret strings from the server as arbitrary code or unrestricted component instructions.
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In either approach, decide which side owns each concern: the server or agent supplies content and intent; the Android app owns visual implementation, local state, validation, and the actions it is willing to perform.
Implement the MCP server around a deliberate feature surface
The Kotlin MCP SDK’s server API provides registration for tools, prompts, and resources. Add only the features the client workflow needs, then declare the corresponding capabilities. A feature declaration tells clients what classes of functionality are available; it does not replace the implementation or the app’s UI contract.
Register tools for specific operations
Give each tool a narrow purpose, a useful description, and an object input schema. For example, an application might expose a tool that requests a particular view of its data rather than one that accepts an unrestricted instruction to build any screen. Validate tool inputs on the server as well as validating UI data on Android.
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Add resources and prompts only when they serve the workflow
Use resources for information the client should be able to read, and prompts for repeatable workflows where that feature is useful. Do not add them merely because the SDK supports them. Keep tool, resource, or prompt logic separate from Compose rendering code; connect a tool result to a UI model through an explicit application boundary.
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1Scan for outdated or missing drivers - takes under a minute2Repair Windows errors before they cause bigger problems3Fix the driver behind crashes, sound loss and screen glitchesThe SDK server module documents addTool, addPrompt, and addResource registration, along with sessions attached to transports and session lifecycle cleanup. Check the SDK documentation and the version you select for the exact API signatures and setup. The API pages reviewed show version 0.15.0; that alone does not establish it as the latest release.
Select a transport for the actual client and host
The Kotlin SDK documents three hosting options in this context. They are alternatives to match to the MCP client and deployment, not interchangeable switches that an Android renderer automatically understands.
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| Transport | Documented use or behavior | Decision to make |
|---|---|---|
| STDIO | Local process communication, suitable for editor- or CLI-style hosting. | Use it when the MCP client launches or manages a local server process. It does not provide a remote Android delivery channel. |
| Ktor SSE | Server-Sent Events with a POST back-channel. | Use it when the chosen client supports this arrangement and a Ktor-hosted network service fits the deployment. |
| Ktor WebSocket | WebSocket hosting through Ktor. | Use it when the client and host support the SDK’s WebSocket option; confirm the exact connection configuration for both sides. |
Before committing to a transport, verify the intended MCP client’s supported connection method and the SDK setup for your chosen version. Separately decide how the Android app receives data: choosing an MCP transport does not define the app’s UI update channel.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Connect server results to Compose state
On Android, keep data access and business logic outside composables. The UI layer should receive application data, transform it into renderable state, display it, and reflect user input back into application state. Compose is Android’s recommended UI toolkit; a composable should render state rather than own server registration or transport lifecycle.
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Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Repair Windows errors before they cause bigger problemsFix Now →- Receive: accept structured UI data through the app’s chosen application boundary.
- Validate: check the protocol or schema version, required fields, component types, property values, and action identifiers before updating visible state.
- Transform: map valid input into the renderer’s supported model and maintain explicit loading, content, and error states.
- Render: have Compose display only supported components using the selected catalog or app-owned mappings.
- Handle actions: route taps and other user input through application logic. Treat action identifiers as requests to perform known operations, not as authorization to execute arbitrary server-provided behavior.
Android’s A2UI renderer describes schema validation, graceful component errors, and reactive updates. Follow those principles even if you choose a custom schema: an invalid component should not silently become a different component or take down the entire screen.
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Plan for invalid data and network exposure
Make rendering failures visible and contained
Define what the app displays when input is malformed, a component is unsupported, or the requested protocol version is incompatible. Keep the failure local where possible—for example, render an explicit error state for the affected content rather than assuming every payload is valid. Log enough information for diagnosis without putting sensitive payload data into logs by default.
Configure Ktor route protections deliberately
The documented Ktor SSE route API enables DNS rebinding protection by default, supports host and origin allowlists, and documents a default maximum incoming request body size of 4 MiB. Configure allowed hosts and origins for the real deployment. The route documentation notes that custom host configuration changes origin-validation behavior; understand that effect before overriding defaults. These route controls do not establish a complete authentication or access-control policy, which must be designed for the service’s environment.
Do not expose a remote MCP service simply because the route starts successfully. Decide who may connect, how clients authenticate, what network boundaries apply, and how sessions and sensitive operations are managed for the actual deployment.
Build and verify in small steps
- Write down the topology: identify the MCP client, Kotlin server, Android app, and any agent or backend. Mark the MCP connection separately from the app’s UI-data path.
- Choose the contract: select the documented A2UI route or define a limited app-owned schema. Record supported versions, components, properties, and actions.
- Pin compatible dependencies: verify current A2UI artifacts and Kotlin SDK versions against official documentation and your Android/Ktor project configuration; do not infer a complete dependency set from artifact names alone.
- Implement the server surface: register only necessary tools, resources, and prompts, with schemas and capabilities aligned to what the client uses.
- Choose one transport: configure the client and server for STDIO, Ktor SSE, or Ktor WebSocket according to the deployment. Add the separate Android delivery path explicitly.
- Implement renderer states: cover loading, valid content, malformed data, unsupported components, and incompatible versions before expanding the catalog.
- Exercise boundaries: test invalid inputs and UI payloads, unknown component and action identifiers, connection loss, and the host/origin policy in the environment where the service will run.
Use View interop only for the cases that need it
If a legacy or SDK-provided Android view has no Compose equivalent, Android documents AndroidView as an interoperability route. Prefer a Compose implementation for custom UI where practical; View interop is a bridge for components that need it, not the default strategy for a new renderer.
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