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Pydantic AI Quickstart

A complete Pydantic AI agent traced with one line. It uses a fake model instead of a real LLM, so it runs without an API key.

Run​

pippip install trace-agent-sdk trace-agent-pydantic-ai
uvuv add trace-agent-sdk trace-agent-pydantic-ai

Start the TraceAgent server at http://127.0.0.1:8000, save the script below as hooks_quickstart.py and run:

python hooks_quickstart.py

The Script​

from pydantic_ai import Agent
from pydantic_ai.messages import ModelResponse, TextPart, ToolCallPart
from pydantic_ai.models.function import FunctionModel
from trace_agent_sdk import TraceAgentClient


def fake_model(messages, info):
    """Stands in for an LLM: asks for the tool first, then answers."""
    if len(messages) == 1:
        return ModelResponse(parts=[ToolCallPart("weather", {"city": "Madrid"})])
    return ModelResponse(parts=[TextPart("It is sunny in Madrid, 23 degrees.")])


# 1. Create the run in TraceAgent.
client = TraceAgentClient("http://127.0.0.1:8000")
run = client.start_run("hooks-quickstart", "What is the weather in Madrid?")

# 2. Your usual agent, plus one line: capabilities=[...]
agent = Agent(
    FunctionModel(fake_model),  # use a real model string, e.g. "openai:gpt-4o", in your own agent
    capabilities=[run.as_pydantic_ai_capability()],  # <-- the TraceAgent line
)


@agent.tool_plain
def weather(city: str) -> str:
    """Return the weather of a city."""
    return f"Sunny, 23 degrees in {city}."


# 3. Use it as always.
result = agent.run_sync("What is the weather in Madrid?")
print(result.output)

# 4. Close the run.
run.finish(result.output)
print(f"Run: {run.run_id}")

Output:

It is sunny in Madrid, 23 degrees.
Run: b34d5d79-198d-4f67-bf66-6815131465bc

What It Does​

  1. Starts a run in the TraceAgent server
  2. Builds a Pydantic AI agent with the TraceAgent capability
  3. The fake model asks for the weather tool, then answers
  4. Finishes the run

Open the run in the UI and you will see these events, in order:

run.started → chain.started → llm.started → llm.completed →
tool.started → tool.succeeded → llm.started → llm.completed →
chain.completed → run.completed

Learn More​

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