Variable RESOURCE_URI_META_KEY`Const`

RESOURCE_URI_META_KEY: "ui/resourceUri"

Metadata key for associating a UI resource URI with a tool.

MCP servers include this key in tool definition metadata (via tools/list) to indicate which UI resource should be displayed when the tool is called. When hosts see a tool with this metadata, they fetch and render the corresponding App.

Note: This constant is provided for reference and backwards compatibility. Server developers should use registerAppTool with the _meta.ui.resourceUri format instead. Host developers must check both formats for compatibility.

Example: Modern format (server-side, not in Apps)

// Preferred: Use registerAppTool with nested ui.resourceUri
registerAppTool(
  server,
  "weather",
  {
    description: "Get weather forecast",
    _meta: {
      ui: { resourceUri: "ui://weather/forecast" },
    },
  },
  handler,
);

Example: Legacy format (deprecated, for backwards compatibility)

// Deprecated: Direct use of RESOURCE_URI_META_KEY
server.registerTool(
  "weather",
  {
    description: "Get weather forecast",
    _meta: {
      [RESOURCE_URI_META_KEY]: "ui://weather/forecast",
    },
  },
  handler,
);

Example: How hosts check for this metadata (must support both formats)

// Hosts should check both modern and legacy formats
const meta = tool._meta;
const uiMeta = meta?.ui as McpUiToolMeta | undefined;
const legacyUri = meta?.[RESOURCE_URI_META_KEY] as string | undefined;
const uiUri = uiMeta?.resourceUri ?? legacyUri;
if (typeof uiUri === "string" && uiUri.startsWith("ui://")) {
  // Fetch the resource and display the UI
}

Variable RESOURCE_URI_META_KEYConst

Example: Modern format (server-side, not in Apps)

Example: Legacy format (deprecated, for backwards compatibility)

Example: How hosts check for this metadata (must support both formats)

Settings

Variable RESOURCE_URI_META_KEY`Const`