diff --git a/llama_stack/providers/inline/agents/meta_reference/agent_instance.py b/llama_stack/providers/inline/agents/meta_reference/agent_instance.py
index 5c492434f..2a93e7b3f 100644
--- a/llama_stack/providers/inline/agents/meta_reference/agent_instance.py
+++ b/llama_stack/providers/inline/agents/meta_reference/agent_instance.py
@@ -610,8 +610,17 @@ class ChatAgent(ShieldRunnerMixin):
                     if event.stop_reason is not None:
                         stop_reason = event.stop_reason
                 span.set_attribute("stop_reason", stop_reason)
-                span.set_attribute("input", [m.model_dump_json() for m in input_messages])
-                span.set_attribute("output", f"content: {content} tool_calls: {tool_calls}")
+                span.set_attribute(
+                    "input",
+                    json.dumps([json.loads(m.model_dump_json()) for m in input_messages]),
+                )
+                output_attr = json.dumps(
+                    {
+                        "content": content,
+                        "tool_calls": [json.loads(t.model_dump_json()) for t in tool_calls],
+                    }
+                )
+                span.set_attribute("output", output_attr)
 
             stop_reason = stop_reason or StopReason.out_of_tokens
 
diff --git a/llama_stack/providers/utils/telemetry/trace_protocol.py b/llama_stack/providers/utils/telemetry/trace_protocol.py
index 924274c42..525ade74d 100644
--- a/llama_stack/providers/utils/telemetry/trace_protocol.py
+++ b/llama_stack/providers/utils/telemetry/trace_protocol.py
@@ -6,6 +6,7 @@
 
 import asyncio
 import inspect
+import json
 from functools import wraps
 from typing import Any, AsyncGenerator, Callable, Type, TypeVar
 
@@ -17,6 +18,10 @@ T = TypeVar("T")
 
 
 def serialize_value(value: Any) -> Primitive:
+    return str(_prepare_for_json(value))
+
+
+def _prepare_for_json(value: Any) -> str:
     """Serialize a single value into JSON-compatible format."""
     if value is None:
         return ""
@@ -25,9 +30,17 @@ def serialize_value(value: Any) -> Primitive:
     elif hasattr(value, "_name_"):
         return value._name_
     elif isinstance(value, BaseModel):
-        return value.model_dump_json()
+        return json.loads(value.model_dump_json())
+    elif isinstance(value, (list, tuple, set)):
+        return [_prepare_for_json(item) for item in value]
+    elif isinstance(value, dict):
+        return {str(k): _prepare_for_json(v) for k, v in value.items()}
     else:
-        return str(value)
+        try:
+            json.dumps(value)
+            return value
+        except Exception:
+            return str(value)
 
 
 def trace_protocol(cls: Type[T]) -> Type[T]:
@@ -104,7 +117,8 @@ def trace_protocol(cls: Type[T]) -> Type[T]:
                     result = method(self, *args, **kwargs)
                     span.set_attribute("output", serialize_value(result))
                     return result
-                except Exception as _e:
+                except Exception as e:
+                    span.set_attribute("error", str(e))
                     raise
 
         if is_async_gen: