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

# Trace PydanticAI applications

LangSmith can capture traces generated by PydanticAI using its built-in OpenTelemetry instrumentation. This guide shows you how to automatically capture traces from your PydanticAI agents and send them to LangSmith for monitoring and analysis.

## Installation

Install the required packages:

<CodeGroup>
  ```bash pip theme={"theme":{"light":"catppuccin-latte","dark":"catppuccin-mocha"}}
  pip install langsmith pydantic-ai opentelemetry-exporter-otlp
  ```

  ```bash uv theme={"theme":{"light":"catppuccin-latte","dark":"catppuccin-mocha"}}
  uv add langsmith pydantic-ai opentelemetry-exporter-otlp
  ```
</CodeGroup>

<Info>
  Requires LangSmith Python SDK version `langsmith>=0.4.26` for optimal OpenTelemetry support.
</Info>

## Setup

### 1. Configure environment variables

Set your [API keys](/langsmith/create-account-api-key) and project name:

```bash theme={"theme":{"light":"catppuccin-latte","dark":"catppuccin-mocha"}}
export LANGSMITH_API_KEY=<your_langsmith_api_key>
export LANGSMITH_PROJECT=<your_project_name>
export OPENAI_API_KEY=<your_openai_api_key>
```

### 2. Configure OpenTelemetry integration

In your PydanticAI application, configure the LangSmith OpenTelemetry integration:

```python theme={"theme":{"light":"catppuccin-latte","dark":"catppuccin-mocha"}}
from langsmith.integrations.otel import configure
from pydantic_ai import Agent

# Configure LangSmith tracing
configure(project_name="pydantic-ai-demo")

# Instrument all PydanticAI agents
Agent.instrument_all()
```

<Note>
  You do not need to set any OpenTelemetry environment variables or configure exporters manually—`configure()` handles everything automatically.
</Note>

### 3. Create and run your PydanticAI agent

Once configured, your PydanticAI agents will automatically send traces to LangSmith:

```python theme={"theme":{"light":"catppuccin-latte","dark":"catppuccin-mocha"}}
from langsmith.integrations.otel import configure
from pydantic_ai import Agent

# Configure LangSmith tracing
configure(project_name="pydantic-ai-demo")

# Instrument all PydanticAI agents
Agent.instrument_all()

# Create and run an agent
agent = Agent('openai:gpt-5.4')
result = agent.run_sync('What is the capital of France?')
print(result.output)
#> Paris
```

## Advanced usage

### Custom metadata and tags

You can add custom metadata to your traces using OpenTelemetry span attributes:

```python theme={"theme":{"light":"catppuccin-latte","dark":"catppuccin-mocha"}}
from opentelemetry import trace
from pydantic_ai import Agent
from langsmith.integrations.otel import configure

configure(project_name="pydantic-ai-metadata")
Agent.instrument_all()

tracer = trace.get_tracer(__name__)

agent = Agent('openai:gpt-5.4')

with tracer.start_as_current_span("pydantic_ai_workflow") as span:
    span.set_attribute("langsmith.metadata.user_id", "user_123")
    span.set_attribute("langsmith.metadata.workflow_type", "question_answering")
    span.set_attribute("langsmith.span.tags", "pydantic-ai,production")

    result = agent.run_sync('Explain quantum computing in simple terms')
    print(result.output)
```

***

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