What’s happening is that your tool is defined as an async generator (because of yield inside async def), so it doesn’t return a single value. Instead, it streams multiple values over time. On the client side, call_tool doesn’t automatically unwrap and consume that stream for you — you need to iterate over it.

Here’s how you can consume the streamed tokens:

result_stream = await self.session.call_tool(
    function_call.name,
    arguments=dict(function_call.args)
)

# `result_stream` is async iterable — loop through it
async for event in result_stream:
    for item in event.content:
        if item.text:
            print(item.text, end="", flush=True)

This way, each yielded chunk from your MCP tool will show up on the client as a separate event, and you can print them in real time as they arrive.

If you just call result.content[0].text, you’re only looking at the first chunk, which explains why you saw the async generator object string.