How to use Agent.to_ag_ui in stdio mode

[RahulDas-dev]

Question

Hi, I'm looking for a way to emit events in stdio mode for Pydantic agents. Specifically, I'd like to capture events such as:

• PartStartEvent
• TextMessageStartEvent
• TextMessageContentEvent
• ToolCallStartEvent
• ToolCallEndEvent
• and Other Events

I've explored using to_ag_ui, but it doesn't seem to support stdio mode. I came across a potential solution in issue #1995, and #2382 which can help me a to implement the same with help of Custom Event Emitter Class.

Before diving into a custom implementation, I'd like to know:

• Are there any better approaches to achieve this?
• Does Pydantic AI have plans to introduce built-in event emitters for accessing streaming data in console and UI integrations?

Any guidance or insights would be greatly appreciated.

Here is my custome Event Emiter Class
https://github.com/RahulDas-dev/Pydantic_developer_agent/blob/main/lib/event_sys/bus.py

Additional Context

No response

[DouweM]

@RahulDas-dev Those AG-UI events are based on the events you get from Agent.iter as documented here: https://ai.pydantic.dev/agents/#streaming. I think that's exactly what you're looking for, but let me know if not and I'll reopen the issue.

[RahulDas-dev]

Thanks for the response. I went through the document you suggested, and with that, my problem can be solved completely. I’ll just need to add some additional code.

But I’m envisioning this as a lightweight event bus using the same AG-UI event format
Agent will emit events to the EVENT BUS in cli mode , or [ to_cli method ]

• Agents emit structured AG-UI events using the EventBus

• Event Bus delivers them over STDIO.

• CLI/Console subscribes to the bus and displays the information in any way the developer chooses.

For reference, here are relevant implementation examples from my framework:

Event bus implementation: - https://github.com/RahulDas-dev/terminallm/tree/v0.3.0/src/event_sys

Agent event emission code: - https://github.com/RahulDas-dev/terminallm/blob/v0.3.0/src/client/content_generator.py

Console subscriber code: - https://github.com/RahulDas-dev/terminallm/blob/v0.3.0/src/console.py

[DouweM]

@RahulDas-dev If you want to use the actual AG-UI events, you can also use run_ag_ui as documented here: https://ai.pydantic.dev/ag-ui/. That'll give you a stream of strs encoded per the accept argument (SSE by default). Outputting those events over stdin would be pretty straightforward.