> ## Documentation Index
> Fetch the complete documentation index at: https://sunpeak.ai/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# MCP Apps getHostCapabilities - Feature Detection

> Read the host's supported capabilities from an MCP App. Use getHostCapabilities for feature detection before calling host-dependent methods like callServerTool, sendMessage, or downloadFile.

<Badge color="green">MCP Apps SDK</Badge>

```ts theme={null}
import { App } from "@modelcontextprotocol/ext-apps";
```

## Overview

`getHostCapabilities()` returns the capabilities the host advertised during the [initialization handshake](/mcp-apps/lifecycle#2-initialization). Use this for feature detection — check whether a capability exists before calling the corresponding method.

Returns `undefined` before `connect()` completes.

## Signature

```ts theme={null}
getHostCapabilities(): McpUiHostCapabilities | undefined
```

## Returns

<ResponseField name="return" type="McpUiHostCapabilities | undefined">
  The host's capabilities, or `undefined` if the app has not connected yet. See [`McpUiHostCapabilities`](/mcp-apps/types/core-types#mcpuihostcapabilities) for the full type definition.
</ResponseField>

## Usage

### Check before calling server tools

```ts theme={null}
await app.connect();

const caps = app.getHostCapabilities();
if (caps?.serverTools) {
  const result = await app.callServerTool({
    name: "get_weather",
    arguments: { location: "Tokyo" },
  });
}
```

### Check before sending messages

```ts theme={null}
if (app.getHostCapabilities()?.message) {
  await app.sendMessage({
    role: "user",
    content: [{ type: "text", text: "Show details" }],
  });
}
```

### Check before downloading files

```ts theme={null}
if (app.getHostCapabilities()?.downloadFile) {
  await app.downloadFile({
    contents: [{
      type: "resource",
      resource: {
        uri: "file:///export.json",
        mimeType: "application/json",
        text: JSON.stringify(data),
      },
    }],
  });
}
```

### Build a capabilities summary

```ts theme={null}
const caps = app.getHostCapabilities();
const features = {
  canCallTools: !!caps?.serverTools,
  canReadResources: !!caps?.serverResources,
  canSendMessages: !!caps?.message,
  canUpdateContext: !!caps?.updateModelContext,
  canOpenLinks: !!caps?.openLinks,
  canDownloadFiles: !!caps?.downloadFile,
  canLog: !!caps?.logging,
};
```

## Capability Fields

| Field                | Enables                                                                                                                                        |
| -------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------- |
| `openLinks`          | [`openLink()`](/mcp-apps/app/requests/open-link)                                                                                               |
| `downloadFile`       | [`downloadFile()`](/mcp-apps/app/requests/download-file)                                                                                       |
| `serverTools`        | [`callServerTool()`](/mcp-apps/app/requests/call-server-tool)                                                                                  |
| `serverResources`    | [`readServerResource()`](/mcp-apps/app/requests/read-server-resource), [`listServerResources()`](/mcp-apps/app/requests/list-server-resources) |
| `logging`            | [`sendLog()`](/mcp-apps/app/requests/send-log)                                                                                                 |
| `updateModelContext` | [`updateModelContext()`](/mcp-apps/app/requests/update-model-context)                                                                          |
| `message`            | [`sendMessage()`](/mcp-apps/app/requests/send-message)                                                                                         |
| `sandbox`            | Host-enforced sandbox permissions and CSP                                                                                                      |

## Related

* [`McpUiHostCapabilities`](/mcp-apps/types/core-types#mcpuihostcapabilities) — Full type definition
* [Capability Detection](/mcp-apps/server/capability-detection) — Server-side capability negotiation
* [Accessors overview](/mcp-apps/app/accessors) — All App accessor methods