Enhance `on_tool_start` Hook to Include Tool Call Arguments

[yanmxa]

Please read this first

• Have you read the docs?Agents SDK docs - Yes
• Have you searched for related issues? Others may have had similar requesrs - Yes

Describe the feature

Currently, the on_tool_start hook in the Agents SDK only provides access to the Agent, Tool (definition), and context, but does not include the actual tool call arguments.

This limitation makes it difficult to trace and debug the agent's lifecycle, as there's no way to inspect the exact parameters passed to the tool before execution.

Proposed Enhancement:

Modify the on_tool_start hook definition to include the tool call arguments, providing full visibility into the tool invocation process.

• Current Definition

async def on_tool_start(
    self,
    context: RunContextWrapper[TContext],
    agent: Agent[TContext],
    tool: Tool,
) -> None:
    """Called before a tool is invoked."""
    pass

• Suggested Update

async def on_tool_start(
    self,
    context: RunContextWrapper[TContext],
    agent: Agent[TContext],
    action: Action, # Include the tool and the tool_call(arguments)
) -> None:
    """Called before a tool is invoked."""
    pass

Why This Improvement Matters:

1. Improved Debugging & Tracing: Developers can log and analyze tool inputs before execution.
2. Greater Flexibility: Hooks can validate or preprocess tool arguments before they are used.
3. More Context for Hooks: Allows hooks to monitor execution flows with full tool call details.

[MrJarnould]

Until the linked PR is accepted, is there any other way to obtain the tool call arguments using hooks before the agent calls the tool?

[vanhtuan0409]

Until the linked PR is accepted, is there any other way to obtain the tool call arguments using hooks before the agent calls the tool?

Some workaround I think of is either using LLM tracing, put logging in tool implement or hijack the network call

[yanmxa]

@MrJarnould @vanhtuan0409 Yes, I do it in the tool calling internal for now. But it's more reasonable to put this in the tracing hook :)

[MrJarnould]

I hope your PR gets reviewed soon!

[Kalai9976]

Any idea when this enhancement will be released ?

[yanmxa]

@rm-openai Could you please take a look at this issue? Thanks!