diff --git a/src/tools/tool.ts b/src/tools/tool.ts
index 5cbb8ac2..a37c7224 100644
--- a/src/tools/tool.ts
+++ b/src/tools/tool.ts
@@ -118,6 +118,7 @@ export abstract class ToolBase {
                 {
                     type: "text",
                     text: `Error running ${this.name}: ${error instanceof Error ? error.message : String(error)}`,
+                    isError: true,
                 },
             ],
         };