Core LLM Observability Concepts

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A span is a unit of work representing an operation in your LLM application, and is the building block of a trace.

Span attributes

A span consists of the following attributes:

  • Name
  • Start time and duration
  • Error type, message, and traceback
  • Inputs and outputs, such as LLM prompts and completions
  • Metadata (for example, LLM parameters such as temperature, max_tokens)
  • Metrics, such as input_tokens and output_tokens
  • Tags

Span kinds

LLM Observability categorizes spans by their span kind, which defines the type of work the span is performing. This can give you more granular insights on what operations are being performed by your LLM application. LLM Observability supports the following span kinds:

  • LLM: A call to an LLM.
  • Workflow: A sequence of operations which include LLM calls and any supporting operations.
  • Agent: A series of decisions and operations made by an autonomous agent.
  • Tool: A call to a program or service where the call arguments are generated by an LLM.
  • Task: Any standalone step in a workflow or agent that does not involve a call to an external service.
  • Embedding: A call to an embedding model or function.
  • Retrieval: A data retrieval operation from an external knowledge base.

To learn more about each span kind, see Span Kinds.


A trace represents the work involved in processing a request in your LLM application, and consists of one or more nested spans. A root span is the first span in a trace, and marks the beginning and end of the trace.

Datadog’s LLM Observability product is designed to support observability for LLM applications with varying complexity. Based on the structure and complexity of your traces, you can unlock the following features of LLM Observability:

1. LLM Inference Monitoring

LLM inference traces are composed of a single LLM span.

A single LLM span

Tracing individual LLM inferences unlocks basic LLM Observability features, allowing you to:

  1. Track inputs and outputs to your LLM calls
  2. Track token usage, error rates, and latencies for your LLM calls
  3. Break down important metrics by model and model provider

The SDK provides integrations to automatically capture LLM calls to specific providers. See Auto-instrumentation for more information. If you are using an LLM provider that is not supported, you must manually instrument your application.

2. LLM Workflow Monitoring

A workflow trace is composed of a root workflow span with nested LLM, task, tool, embedding, and retrieval spans.

A trace visualizing a more complex LLM workflow

Most LLM applications include operations that surround LLM calls and play a large role in your overall application performance - for example, tool calls to external APIs or preprocessing task steps.

By tracing LLM calls and contextual task or tool operations together under workflow spans, you can unlock more granular insights and a more holistic view of your LLM application.

3. LLM Agent Monitoring

An agent monitoring trace is composed of a root agent span with nested LLM, task, tool, embedding, retrieval, and workflow spans.

A trace visualizing an LLM agent

If your LLM application has complex autonomous logic, such as decision-making that can’t be captured by a static workflow, you are likely using an LLM Agent. Agents may execute multiple different workflows depending on the user input.

You can instrument your LLM application to trace and group together all workflows and contextual operations run by a single LLM agent as an agent trace.


Evaluations are a method for measuring the performance of your LLM application. For example, quality checks like failure to answer or topic relevancy are different types of evaluations that you can track for your LLM application.

Datadog’s LLM Observability associates evaluations with individual spans so that you can view the inputs and outputs that led to a specific evaluation. Datadog provides a few out-of-the-box evaluations for your traces, but you can also submit your own evaluations to LLM Observability (see the Evaluations guide for more information).