diff --git a/src/types.ts b/src/types.ts
index 64153094d..9828ff039 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -944,49 +944,51 @@ export const PromptListChangedNotificationSchema = NotificationSchema.extend({
  * Clients should never make tool use decisions based on ToolAnnotations
  * received from untrusted servers.
  */
-export const ToolAnnotationsSchema = z.object({
-    /**
-     * A human-readable title for the tool.
-     */
-    title: z.string().optional(),
+export const ToolAnnotationsSchema = z
+    .object({
+        /**
+         * A human-readable title for the tool.
+         */
+        title: z.string().optional(),
 
-    /**
-     * If true, the tool does not modify its environment.
-     *
-     * Default: false
-     */
-    readOnlyHint: z.boolean().optional(),
+        /**
+         * If true, the tool does not modify its environment.
+         *
+         * Default: false
+         */
+        readOnlyHint: z.boolean().optional(),
 
-    /**
-     * If true, the tool may perform destructive updates to its environment.
-     * If false, the tool performs only additive updates.
-     *
-     * (This property is meaningful only when `readOnlyHint == false`)
-     *
-     * Default: true
-     */
-    destructiveHint: z.boolean().optional(),
+        /**
+         * If true, the tool may perform destructive updates to its environment.
+         * If false, the tool performs only additive updates.
+         *
+         * (This property is meaningful only when `readOnlyHint == false`)
+         *
+         * Default: true
+         */
+        destructiveHint: z.boolean().optional(),
 
-    /**
-     * If true, calling the tool repeatedly with the same arguments
-     * will have no additional effect on the its environment.
-     *
-     * (This property is meaningful only when `readOnlyHint == false`)
-     *
-     * Default: false
-     */
-    idempotentHint: z.boolean().optional(),
+        /**
+         * If true, calling the tool repeatedly with the same arguments
+         * will have no additional effect on the its environment.
+         *
+         * (This property is meaningful only when `readOnlyHint == false`)
+         *
+         * Default: false
+         */
+        idempotentHint: z.boolean().optional(),
 
-    /**
-     * If true, this tool may interact with an "open world" of external
-     * entities. If false, the tool's domain of interaction is closed.
-     * For example, the world of a web search tool is open, whereas that
-     * of a memory tool is not.
-     *
-     * Default: true
-     */
-    openWorldHint: z.boolean().optional()
-});
+        /**
+         * If true, this tool may interact with an "open world" of external
+         * entities. If false, the tool's domain of interaction is closed.
+         * For example, the world of a web search tool is open, whereas that
+         * of a memory tool is not.
+         *
+         * Default: true
+         */
+        openWorldHint: z.boolean().optional()
+    })
+    .catchall(z.unknown());
 
 /**
  * Definition for a tool the client can call.