`tool_output` stream events don't distinguish between success and error states

[habema]

Problem

When an agent invokes a tool, the tool_output stream event always has the same structure regardless of whether the tool succeeded or failed. Both successful results and error messages end up in the output field with no indication of which is which.

This makes it impossible for a UI to properly present tool execution results - it can't tell if the output represents a successful tool result or an error message.

Current Behavior

RunItemStreamEvent(
    name="tool_output",
    item=ToolCallOutputItem(
        output="some result",  # Could be success OR error message
        raw_item={...},
        agent=agent
    )
)

My question; is this behavior intentional? Are there design reasons for not distinguishing success/error states? Is extending the ToolCallOutputItem data model to have an is_error flag a welcome contribution?

[seratch]

I haven't verified this yet, but once I am done with other tasks, I will check this in depth.

[habema]

Sure. Here is a code snippet to help you test this:

import asyncio

from agents import Agent, RunItemStreamEvent, Runner, ToolCallOutputItem, function_tool


@function_tool
def get_current_weather(city: str) -> str:
    """Get the current weather for a given city"""
    raise Exception("Not implemented")

async def main():
    agent = Agent(
        name="Weather Agent",
        model="gpt-4.1-mini",
        tools=[get_current_weather],
    )

    result = Runner.run_streamed(agent, input="Get the current weather in Tokyo")
    async for event in result.stream_events():
        if isinstance(event, RunItemStreamEvent) and isinstance(event.item, ToolCallOutputItem):
            print(event.item)

if __name__ == "__main__":
    asyncio.run(main())