MCP Run Python README

How Python does AI

Agents, realtime voice, image generation, embeddings. Every model, every interface, typed end to end.

Pydantic AI is the Python AI SDK: a typed, extensible agent loop with every model a string swap away. The same agent runs everywhere you need it: behind a web frontend, in the terminal, on a voice call, on a durable background queue, or as a plain object you call run() on. Image generation and embeddings come in the same box.

Pydantic AI Harness has everything an agent needs for complex, long-running work, snapped on as capabilities, from memory, sub-agents, and context management to a complete coding agent.

View the complete documentation at pydantic.dev/docs/ai.

What are you building?

From simple typed data extraction to complex, long-running multi-agent collaboration, Pydantic AI and Pydantic AI Harness have got you covered.

Coding agent

A complete coding agent in your terminal: workspace-rooted file access, allowlisted shell, repo orientation, planning, and context management that survives long sessions. Here with web search and a second-opinion advisor snapped on alongside:

bash

uv add pydantic-ai pydantic-ai-harness

server.ts

from pydantic_ai import Agent
from pydantic_ai.capabilities import WebSearch
from pydantic_ai_harness import Advisor, Coder

agent = Agent(
    'anthropic:claude-fable-5',
    capabilities=[
        Coder(),  # files, shell, repo context, planning, sub-agents, context management
        WebSearch(),  # look up docs and error messages on the web
        Advisor('openai:gpt-5.6-sol'),  # a second opinion from another model when stuck
    ],
)
agent.to_cli_sync()

Coder is a regular combined capability, not a black box: use it whole, or use the blocks it bundles directly; the two are equivalent:

python

capabilities = [
    FileSystem('.'), Shell(cwd='.'), RepoContext(), Planning(), SubAgents(...),
    ClearToolResults(), WarnNearLimits(), ToolOutputLimits(),
]

Run the file and you're chatting with the agent in your terminal. To try it before writing any code, run the exported coder_agent with clai (the Pydantic AI CLI), via uvx:

bash

uvx --with pydantic-ai-harness clai -a pydantic_ai_harness.coder:coder_agent -m anthropic:claude-fable-5

Build this → Coder, from the Harness

Data extraction

Give the agent an output type and tools, and every run comes back validated and typed:

bash

uv add pydantic-ai

server.ts

from typing import Literal

from pydantic import BaseModel, Field

from pydantic_ai import Agent, RunContext


class Sentiment(BaseModel):
    label: Literal['positive', 'negative', 'neutral']
    score: float = Field(ge=-1, le=1)


agent = Agent('openai:gpt-5.6-sol', output_type=Sentiment)


@agent.tool
def recent_reviews(ctx: RunContext[None], product: str) -> list[str]:
    """Fetch recent review snippets for a product."""
    return ['The new release fixed everything I complained about!']


result = agent.run_sync('How are people feeling about the Extract app?')
print(result.output)
#> label='positive' score=0.9

The @agent.tool function receives a RunContext that carries your dependencies in; the rest of its signature and its docstring become the tool schema, arguments are validated before your code runs, and the run is guaranteed to return a Sentiment, so your IDE, type checker, and the LLM all agree on the returned type.

Build this → Agents, Function Tools, and Structured Output

Durable workflow

Attach TemporalDurability and the same agent runs inside a Temporal workflow under durable execution: every model and tool call becomes a durable activity, so a run working through a background queue survives restarts, failures, and long waits:

bash

uv add "pydantic-ai[temporal]"

server.ts

from temporalio import workflow

from pydantic_ai import Agent
from pydantic_ai.capabilities import WebFetch, WebSearch
from pydantic_ai.durable_exec.temporal import PydanticAIWorkflow, TemporalDurability

agent = Agent(
    'openai:gpt-5.6-sol',
    instructions='Research the topic and write a structured brief.',
    name='researcher',
    capabilities=[WebSearch(), WebFetch(), TemporalDurability()],
)


@workflow.defn
class ResearchWorkflow(PydanticAIWorkflow):
    __pydantic_ai_agents__ = [agent]

    @workflow.run
    async def run(self, topic: str) -> str:
        result = await agent.run(f'Write a brief on: {topic}')
        return result.output

DBOS and Prefect attach the same way, first-party and co-maintained, with Restate, Kitaru, and Airflow integrations besides.

Build this → Durable Execution

Realtime voice

Put the same agent on a live voice session, tools and capabilities included:

bash

uv add "pydantic-ai[openai-realtime]"

server.ts

import asyncio

from pydantic_ai import Agent
from pydantic_ai.capabilities import MCP

agent = Agent(
    instructions='You are a helpful voice assistant.',
    capabilities=[MCP('https://internal.example.com/mcp')],  # capabilities work in voice too
)

@agent.tool_plain
def order_status(order_id: str) -> str:
    """Look up the status of an order."""
    return f'Order {order_id}: shipped, arriving Thursday.'

async with agent.realtime('openai:gpt-realtime-2.1').session() as session:
    microphone = asyncio.create_task(session.send_audio(microphone_chunks()))  # your microphone → the model
    speaker = asyncio.create_task(play_audio(session.stream_audio()))  # model audio → your speaker
    async for part in session.stream_transcripts():
        print(f'{part.speaker}: {part.transcript}')

The model calls your tools mid-conversation while it keeps talking, and every session is instrumented; voice is just another frontend, on OpenAI Realtime, Gemini Live, Azure, and xAI Grok Voice.

Build this → Realtime Voice

Image generation

Generate an image with a dedicated image model, no agent run required:

bash

uv add pydantic-ai

server.ts

from pathlib import Path

from pydantic_ai import ImageGenerator

generator = ImageGenerator('openai:gpt-image-2')
result = generator.generate_sync('A minimalist logo for a coffee shop called Extract.')
Path('logo.png').write_bytes(result.image.data)

That standalone image API is for when your application decides; when an agent run decides, there is provider-native generation with output_type=BinaryImage for a typed image output, and the ImageGeneration capability with its fallbacks for models that generate no images of their own.

Build this → Image Generation

Why Pydantic AI

Any model, one Python API. Virtually every model and provider (OpenAI, Anthropic, Google, Bedrock, Azure AI Foundry, Groq, Mistral, xAI, Ollama, and dozens more), swappable with a string, or through the Pydantic AI Gateway: one key for all of them, with failover and cost monitoring built in. No flagship feature is locked to one vendor.
Typed end to end. Structured outputs, typed dependency injection, typed tools: your IDE, type checker, and coding agent all know what your agent returns, moving whole classes of errors from runtime to write-time. When plain control flow isn't enough, Pydantic Graph brings the same typing to graph-based workflows.
Measured, not vibes. OpenTelemetry-native instrumentation works with any OTel backend; one line lights up Pydantic Logfire for real-time debugging, tracing, and cost tracking backed by genai-prices. Pydantic Evals tests agent behavior the way pytest tests code.
Batteries, composably. One primitive, the capability, bundles tools, instructions, hooks, and model settings into reusable units. Core ships fundamentals like MCP and web search, the Harness ships everything else, and complete agents like Coder and Researcher are just capabilities composed: they come apart the way they went together. Or skip code entirely with YAML/JSON agent specs.
Every interface. One agent definition runs as a CLI, a built-in web chat, or realtime speech (OpenAI Realtime, Gemini Live, Azure, xAI Grok Voice); UI event streams (AG-UI, Vercel AI) connect it to your own frontend or anything else; and ACP (experimental) serves it as an editor agent.
Durable execution. First-party, co-maintained durable execution on Temporal, DBOS, Prefect, and Restate, plus external SDK integrations for Kitaru and Airflow. Agents survive restarts and run for days on the engine you already operate, with human-in-the-loop approval built in.

Built by the Pydantic team: Pydantic Validation is the validation layer of the OpenAI SDK, the Anthropic SDK, the Google ADK, LangChain, and most of the AI ecosystem (and the foundation FastAPI was built on). Pydantic AI brings that same feeling to agents.

Putting it together: a bank support agent

A typed support agent showing several features working together: dependency injection, function tools, structured output, a reusable capability bundling the customer context, and an on-demand capability the model loads only when the conversation calls for it:

server.ts

from dataclasses import dataclass

from pydantic import BaseModel, Field

from pydantic_ai import Agent, Capability, RunContext

from bank_database import DatabaseConn


@dataclass
class SupportDependencies:  # inject any client: DB pools, HTTP APIs, user info
    customer_id: int
    db: DatabaseConn


class SupportOutput(BaseModel):
    support_advice: str = Field(description='Advice returned to the customer')
    block_card: bool = Field(description="Whether to block the customer's card")
    risk: int = Field(description='Risk level of query', ge=0, le=10)


customer_context = Capability[SupportDependencies](  # a reusable unit of tools + instructions
    id='customer-context',
    description="Who the customer is and what's on their account.",
)


@customer_context.instructions
async def add_customer_name(ctx: RunContext[SupportDependencies]) -> str:
    customer_name = await ctx.deps.db.customer_name(id=ctx.deps.customer_id)
    return f"The customer's name is {customer_name!r}"


@customer_context.tool  # signature and docstring become the tool schema the LLM sees
async def customer_balance(
    ctx: RunContext[SupportDependencies], include_pending: bool
) -> float:
    """Returns the customer's current account balance."""
    return await ctx.deps.db.customer_balance(
        id=ctx.deps.customer_id,
        include_pending=include_pending,
    )


refunds = Capability[SupportDependencies](  # deferred: loads on demand, like a skill
    id='refunds',
    description='Refund eligibility and refund status.',
    defer_loading=True,
)


@refunds.tool
async def refund_status(ctx: RunContext[SupportDependencies]) -> str:
    """Look up the refund status for the customer's most recent charge."""
    return await ctx.deps.db.refund_status(id=ctx.deps.customer_id)


support_agent = Agent(
    'openai:gpt-5.6-sol',
    deps_type=SupportDependencies,
    output_type=SupportOutput,  # the run returns a validated SupportOutput, typed as such
    instructions=(
        'You are a support agent in our bank, give the '
        'customer support and judge the risk level of their query.'
    ),
    capabilities=[customer_context, refunds],
)


...  # in a real use case: more tools, longer instructions


async def main():
    deps = SupportDependencies(customer_id=123, db=DatabaseConn())
    result = await support_agent.run('What is my balance?', deps=deps)
    print(result.output)
    """
    support_advice='Hello John, your current account balance, including pending transactions, is $123.45.' block_card=False risk=1
    """

    result = await support_agent.run('I just lost my card!', deps=deps)
    print(result.output)
    """
    support_advice="I'm sorry to hear that, John. We are temporarily blocking your card to prevent unauthorized transactions." block_card=True risk=8
    """

    result = await support_agent.run(  # the model loads `refunds` on demand, then answers
        'Was I refunded for the duplicate charge on my last statement?', deps=deps
    )
    print(result.output)
    """
    support_advice='Good news, John: the duplicate charge on your last statement was refunded on 2026-05-01.' block_card=False risk=1
    """

For the annotated walkthrough and Logfire tracing, see the same example in the docs.

Next Steps

Install Pydantic AI and put your own coding agent to work: install the Pydantic AI skill, point it at the examples and the Harness index, and tell it what you'd like to build. No API key needed to start (there's a built-in 'test' model).
Read the docs and the API reference.
Give your agent its batteries: Pydantic AI Harness.
Join Slack or file an issue on GitHub.

Part of the Pydantic Stack

Everything you need to ship production-grade AI agents:

Pydantic AI: the type-safe AI SDK
Pydantic AI Harness: the official capability library and harness, from single capabilities to complete agents
Pydantic Logfire: AI-first, full-stack observability
Logfire AI Gateway: unified LLM proxy
Pydantic Evals: evaluate any Python function, agents included, with production evals on Logfire
Pydantic Graph: typed graph control flow
genai-prices: model pricing data, kept current