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MCP Apps SDK 
import type {
  McpUiHostContext,
  McpUiHostCapabilities,
  McpUiAppCapabilities,
  McpUiClientCapabilities,
  McpUiTheme,
  McpUiDisplayMode,
  McpUiStyles,
  McpUiStyleVariableKey,
  McpUiHostStyles,
  McpUiHostCss,
  McpUiToolMeta,
  McpUiToolVisibility,
  McpUiResourceMeta,
  McpUiResourceCsp,
  McpUiResourcePermissions,
  McpUiSupportedContentBlockModalities,
} from "@modelcontextprotocol/ext-apps";

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McpUiHostContext

Rich context about the host environment, provided during initialization and updated via onhostcontextchanged. 
interface McpUiHostContext {
  toolInfo?: {
    id?: RequestId;
    tool: Tool;
  };
  theme?: McpUiTheme;
  styles?: McpUiHostStyles;
  displayMode?: McpUiDisplayMode;
  availableDisplayModes?: McpUiDisplayMode[];
  containerDimensions?: {
    width?: number;     // pixels
    maxWidth?: number;  // pixels
    height?: number;    // pixels
    maxHeight?: number; // pixels
  };
  locale?: string;           // BCP 47 format (e.g., "en-US")
  timeZone?: string;         // IANA format (e.g., "America/New_York")
  userAgent?: string;        // Host application identifier
  platform?: "web" | "desktop" | "mobile";
  deviceCapabilities?: {
    touch?: boolean;
    hover?: boolean;
  };
  safeAreaInsets?: {
    top: number;    // pixels
    right: number;  // pixels
    bottom: number; // pixels
    left: number;   // pixels
  };
}

​
McpUiHostCapabilities

Capabilities supported by the host, received during initialization. 
interface McpUiHostCapabilities {
  experimental?: {};
  openLinks?: {};
  downloadFile?: {};
  serverTools?: { listChanged?: boolean };
  serverResources?: { listChanged?: boolean };
  logging?: {};
  sandbox?: {
    permissions?: McpUiResourcePermissions;
    csp?: McpUiResourceCsp;
  };
  updateModelContext?: McpUiSupportedContentBlockModalities;
  message?: McpUiSupportedContentBlockModalities;
}
FieldDescription
openLinksHost supports openLink()
downloadFileHost supports downloadFile()
serverToolsHost can proxy callServerTool() to the MCP server
serverResourcesHost can proxy readServerResource() to the MCP server
loggingHost accepts sendLog() messages
sandboxPermissions and CSP applied by the host
updateModelContextHost accepts updateModelContext()
messageHost accepts sendMessage()

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McpUiAppCapabilities

Capabilities provided by the View, sent during initialization. 
interface McpUiAppCapabilities {
  experimental?: {};
  tools?: { listChanged?: boolean };
  availableDisplayModes?: McpUiDisplayMode[];
}
FieldDescription
toolsApp exposes tools that the host can call via oncalltool
availableDisplayModesDisplay modes the app supports

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McpUiClientCapabilities

Advertised by hosts to servers via the MCP extensions field. Used with getUiCapability(). 
interface McpUiClientCapabilities {
  mimeTypes?: string[];  // Must include "text/html;profile=mcp-app"
}

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McpUiTheme

type McpUiTheme = "light" | "dark";
The sunpeak framework also exports a short alias: Theme (equivalent to McpUiTheme).

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McpUiDisplayMode

type McpUiDisplayMode = "inline" | "fullscreen" | "pip";
The sunpeak framework also exports a short alias: DisplayMode (equivalent to McpUiDisplayMode).

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McpUiHostStyles

interface McpUiHostStyles {
  variables?: McpUiStyles;
  css?: McpUiHostCss;
}

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McpUiHostCss

interface McpUiHostCss {
  fonts?: string;  // @font-face rules or @import statements
}

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McpUiStyles

A record mapping CSS variable names to string values. All keys are optional. 
type McpUiStyles = Record<McpUiStyleVariableKey, string | undefined>;
See CSS Variables for the full list of variable keys.

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McpUiToolMeta

UI metadata for tools, set in _meta.ui of tool configuration. 
interface McpUiToolMeta {
  resourceUri?: string;
  visibility?: McpUiToolVisibility[];  // Default: ["model", "app"]
}

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McpUiToolVisibility

type McpUiToolVisibility = "model" | "app";

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McpUiResourceMeta

UI metadata for resources, set in _meta.ui of resource content items. 
interface McpUiResourceMeta {
  csp?: McpUiResourceCsp;
  permissions?: McpUiResourcePermissions;
  domain?: string;
  prefersBorder?: boolean;
}

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McpUiResourceCsp

Content Security Policy configuration. 
interface McpUiResourceCsp {
  connectDomains?: string[];     // fetch/XHR/WebSocket origins
  resourceDomains?: string[];    // img/script/style/font/media origins
  frameDomains?: string[];       // Nested iframe origins
  baseUriDomains?: string[];     // Allowed base URIs
}

​
McpUiResourcePermissions

Browser capabilities requested by the resource. 
interface McpUiResourcePermissions {
  camera?: {};
  microphone?: {};
  geolocation?: {};
  clipboardWrite?: {};
}

​
McpUiSupportedContentBlockModalities

Content block types supported by the host for sendMessage and updateModelContext. 
interface McpUiSupportedContentBlockModalities {
  text?: {};
  image?: {};
  audio?: {};
  resource?: {};
  resourceLink?: {};
  structuredContent?: {};
}
The sunpeak framework provides convenience hooks for accessing these types reactively: useHostContext, useHostInfo, and useTheme.