`RealtimeToolStart` events do not expose tool arguments/input parameters

[KelSolaar]

Description

When using the OpenAI agents library (v0.2.9) with realtime sessions, the tool_start events do not include the arguments/parameters being passed to the tool. This makes it impossible to display tool inputs in the UI, limiting visibility into what operations are being performed.

Current Behavior

• tool_start events only contain: agent, tool, info, and type attributes
• The info attribute contains only context with usage metrics
• Tool arguments are passed to the MCP server (visible in debug logs from overridden call_tool method) but not exposed in the event object
• No apparent way to access the input parameters from the RealtimeToolStart event

Expected Behavior

• tool_start events should include an arguments or input field containing the parameters being passed to the tool
• This would allow UIs to display what inputs are being processed, similar to how tool_end events expose the output/results

Example of desired behavior:

# Current tool_end event (working):
{
    "type": "tool_end",
    "tool": "AddNumbers",
    "output": '{"result": 42}'
}

# Desired tool_start event (not currently available):
{
    "type": "tool_start", 
    "tool": "AddNumbers",
    "arguments": {"a": 15, "b": 27}  # <-- This is missing
}

Environment

• openai-agents version: 0.2.9
• Python version: 3.13.2
• Use case: Realtime agent cohort with MCP server integration

[ruskaruma]

Greetings, @seratch and @KelSolaar .
I’d like to work on this issue if no one is currently assigned to it. Please let me know if it’s available.