> ## 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.

# trace

> Decorator for automatic function tracing with input/output capture.

<Info>Re-exported from [`fiddler_otel.decorators.trace`](/sdk-api/otel/trace).</Info>

Decorator for automatic function tracing with input/output capture.

Uses the global FiddlerClient when `client=` is not passed.
Supports both sync and async functions.

## Parameters

<ParamField path="func" type="Callable | None" required={false} default="None">
  Function to decorate.
</ParamField>

<ParamField path="name" type="str | None" required={false} default="None">
  Custom span name (defaults to the function name).
</ParamField>

<ParamField path="as_type" type="Literal['span', 'generation', 'chain', 'tool']" required={false} default="'span'">
  Span type — `"span"`, `"generation"`, `"chain"`, or `"tool"`.
</ParamField>

<ParamField path="capture_input" type="bool" required={false} default="True">
  Capture function arguments as span input.
</ParamField>

<ParamField path="capture_output" type="bool" required={false} default="True">
  Capture the return value as span output.
</ParamField>

<ParamField path="client" type="FiddlerClient | None" required={false} default="get_client()">
  FiddlerClient instance (defaults to `get_client()`).
</ParamField>

<ParamField path="model" type="str | None" required={false} default="None">
  LLM model name; sets `gen_ai.request.model`.
</ParamField>

<ParamField path="user_id" type="str | None" required={false} default="None">
  User identifier; sets `user.id`.
</ParamField>

<ParamField path="version" type="str | None" required={false} default="None">
  Version string; sets `service.version`.
</ParamField>

<ParamField path="system" type="str | None" required={false} default="None">
  LLM provider; sets `gen_ai.system`.
</ParamField>

## Returns

<ResponseField type="Callable">
  The decorated function.
</ResponseField>

<Info>See the [canonical reference](/sdk-api/otel/trace) for the full description and examples.</Info>