diff --git a/src/spec.types.ts b/src/spec.types.ts
index f97a0a6f..4f829ccb 100644
--- a/src/spec.types.ts
+++ b/src/spec.types.ts
@@ -548,3 +548,46 @@ export interface McpUiToolMeta {
    */
   visibility?: McpUiToolVisibility[];
 }
+
+/**
+ * Method string constants for MCP Apps protocol messages.
+ *
+ * These constants provide a type-safe way to check message methods without
+ * accessing internal Zod schema properties. External libraries should use
+ * these constants instead of accessing `schema.shape.method._def.values[0]`.
+ *
+ * @example
+ * ```typescript
+ * import { SANDBOX_PROXY_READY_METHOD } from '@modelcontextprotocol/ext-apps';
+ *
+ * if (event.data.method === SANDBOX_PROXY_READY_METHOD) {
+ *   // Handle sandbox proxy ready notification
+ * }
+ * ```
+ */
+export const OPEN_LINK_METHOD: McpUiOpenLinkRequest["method"] = "ui/open-link";
+export const MESSAGE_METHOD: McpUiMessageRequest["method"] = "ui/message";
+export const SANDBOX_PROXY_READY_METHOD: McpUiSandboxProxyReadyNotification["method"] =
+  "ui/notifications/sandbox-proxy-ready";
+export const SANDBOX_RESOURCE_READY_METHOD: McpUiSandboxResourceReadyNotification["method"] =
+  "ui/notifications/sandbox-resource-ready";
+export const SIZE_CHANGED_METHOD: McpUiSizeChangedNotification["method"] =
+  "ui/notifications/size-changed";
+export const TOOL_INPUT_METHOD: McpUiToolInputNotification["method"] =
+  "ui/notifications/tool-input";
+export const TOOL_INPUT_PARTIAL_METHOD: McpUiToolInputPartialNotification["method"] =
+  "ui/notifications/tool-input-partial";
+export const TOOL_RESULT_METHOD: McpUiToolResultNotification["method"] =
+  "ui/notifications/tool-result";
+export const TOOL_CANCELLED_METHOD: McpUiToolCancelledNotification["method"] =
+  "ui/notifications/tool-cancelled";
+export const HOST_CONTEXT_CHANGED_METHOD: McpUiHostContextChangedNotification["method"] =
+  "ui/notifications/host-context-changed";
+export const RESOURCE_TEARDOWN_METHOD: McpUiResourceTeardownRequest["method"] =
+  "ui/resource-teardown";
+export const INITIALIZE_METHOD: McpUiInitializeRequest["method"] =
+  "ui/initialize";
+export const INITIALIZED_METHOD: McpUiInitializedNotification["method"] =
+  "ui/notifications/initialized";
+export const REQUEST_DISPLAY_MODE_METHOD: McpUiRequestDisplayModeRequest["method"] =
+  "ui/request-display-mode";
diff --git a/src/types.ts b/src/types.ts
index d710ad35..da4a71fa 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -12,6 +12,20 @@
 // Re-export all types from spec.types.ts
 export {
   LATEST_PROTOCOL_VERSION,
+  OPEN_LINK_METHOD,
+  MESSAGE_METHOD,
+  SANDBOX_PROXY_READY_METHOD,
+  SANDBOX_RESOURCE_READY_METHOD,
+  SIZE_CHANGED_METHOD,
+  TOOL_INPUT_METHOD,
+  TOOL_INPUT_PARTIAL_METHOD,
+  TOOL_RESULT_METHOD,
+  TOOL_CANCELLED_METHOD,
+  HOST_CONTEXT_CHANGED_METHOD,
+  RESOURCE_TEARDOWN_METHOD,
+  INITIALIZE_METHOD,
+  INITIALIZED_METHOD,
+  REQUEST_DISPLAY_MODE_METHOD,
   type McpUiTheme,
   type McpUiDisplayMode,
   type McpUiStyleVariableKey,