Document that callback parameter names must match exactly (e.g., callback_context, not ctx)

[irskid5]

Summary

The callback documentation shows examples with specific parameter names like callback_context and llm_request, but doesn't explicitly state that these exact names are required. Users may assume they can use any parameter name (e.g., ctx instead of callback_context), leading to confusing runtime errors.

Problem

When defining a callback with a different parameter name:

async def my_callback(ctx: CallbackContext) -> Optional[types.Content]:
    # ...

The callback fails at runtime with:

TypeError: my_callback() got an unexpected keyword argument 'callback_context'

This happens because ADK invokes callbacks using keyword arguments:

callback(callback_context=callback_context, llm_request=llm_request)

Expected Behavior

The documentation should explicitly state that callback parameter names must match the expected names exactly, such as:

• callback_context (not ctx, context, etc.)
• llm_request / llm_response
• tool, args, tool_context, tool_response

Suggested Fix

Add a note to the Callbacks documentation or Types of Callbacks page, such as:

Important: Callback parameter names must match exactly as shown in the examples. ADK invokes callbacks using keyword arguments, so using different parameter names (e.g., ctx instead of callback_context) will result in a TypeError.

Affected Pages

• https://google.github.io/adk-docs/callbacks/
• https://google.github.io/adk-docs/callbacks/types-of-callbacks/