> ## Documentation Index
> Fetch the complete documentation index at: https://docs.fiddler.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# StrandsSpanProcessor

> Propagates parent attributes via `CoreFiddlerSpanProcessor` plus Strands-specific behavior.

Propagates parent attributes via `CoreFiddlerSpanProcessor` plus Strands-specific behavior.

On every span start this processor:

1. Delegates to `CoreFiddlerSpanProcessor` for standard attribute denormalization.
2. For `chat` spans only: copies the parent's `system_prompt` into a
   `gen_ai.system.message` event as a workaround for Strands not always emitting
   that event on the chat span upstream (strands-agents/sdk-python#822).

## on\_start()

Called when a span starts. Automatically propagates attributes from parent.

### Parameters

<ParamField path="span" type="Span" required={true}>
  The span being started.
</ParamField>

<ParamField path="parent_context" type="Context | None" required={false} default="None">
  The parent context, if any.
</ParamField>