diff --git a/x-pack/platform/plugins/shared/onechat/server/services/agents/modes/utils/to_langchain_messages.test.ts b/x-pack/platform/plugins/shared/onechat/server/services/agents/modes/utils/to_langchain_messages.test.ts
index 0d90d0fb48e6c..a23d78ea9b72a 100644
--- a/x-pack/platform/plugins/shared/onechat/server/services/agents/modes/utils/to_langchain_messages.test.ts
+++ b/x-pack/platform/plugins/shared/onechat/server/services/agents/modes/utils/to_langchain_messages.test.ts
@@ -92,12 +92,14 @@ describe('conversationLangchainMessages', () => {
     expect((toolCallAIMessage as AIMessage).tool_calls![0].id).toBe('call-1');
     // ToolMessage type guard is not imported, so just check property
     expect((toolCallToolMessage as ToolMessage).tool_call_id).toBe('call-1');
-    expect(toolCallToolMessage.content).toEqual([
-      {
-        type: ToolResultType.other,
-        data: 'result!',
-      },
-    ]);
+    expect(toolCallToolMessage.content).toEqual(
+      JSON.stringify([
+        {
+          type: ToolResultType.other,
+          data: 'result!',
+        },
+      ])
+    );
     expect(isAIMessage(assistantMessage)).toBe(true);
     expect(assistantMessage.content).toBe('done!');
     expect(isHumanMessage(nextHumanMessage)).toBe(true);
@@ -146,7 +148,9 @@ describe('conversationLangchainMessages', () => {
     expect((toolCallAIMessage as AIMessage).tool_calls).toHaveLength(1);
     expect((toolCallAIMessage as AIMessage).tool_calls![0].id).toBe('call-2');
     expect((toolCallToolMessage as ToolMessage).tool_call_id).toBe('call-2');
-    expect(toolCallToolMessage.content).toEqual([{ type: ToolResultType.other, data: 'found!' }]);
+    expect(toolCallToolMessage.content).toEqual(
+      JSON.stringify([{ type: ToolResultType.other, data: 'found!' }])
+    );
     expect(isAIMessage(secondAssistantMessage)).toBe(true);
     expect(secondAssistantMessage.content).toBe('done with bar');
     expect(isHumanMessage(lastHumanMessage)).toBe(true);
diff --git a/x-pack/platform/plugins/shared/onechat/server/services/agents/modes/utils/to_langchain_messages.ts b/x-pack/platform/plugins/shared/onechat/server/services/agents/modes/utils/to_langchain_messages.ts
index 2991354814c63..db21c5c92f29f 100644
--- a/x-pack/platform/plugins/shared/onechat/server/services/agents/modes/utils/to_langchain_messages.ts
+++ b/x-pack/platform/plugins/shared/onechat/server/services/agents/modes/utils/to_langchain_messages.ts
@@ -83,7 +83,7 @@ export const createToolCallMessages = (toolCall: ToolCallWithResult): [AIMessage
 
   const toolResultMessage = new ToolMessage({
     tool_call_id: toolCall.tool_call_id,
-    content: toolCall.results,
+    content: JSON.stringify(toolCall.results),
   });
 
   return [toolCallMessage, toolResultMessage];