Command Line Interface (CLI)

Pydantic AI comes with a CLI, clai (pronounced “clay”). You can use it to chat with various LLMs and quickly get answers, right from the command line, or spin up a uvicorn server to chat with your Pydantic AI agents from your browser.

Installation

You can run the clai using uvx:

Terminal

uvx clai

Or install clai globally with uv:

Terminal

uv tool install clai
...
clai

Or with pip:

Terminal

pip install clai
...
clai

CLI Usage

You’ll need to set an environment variable depending on the provider you intend to use.

E.g. if you’re using OpenAI, set the OPENAI_API_KEY environment variable:

Terminal

export OPENAI_API_KEY='your-api-key-here'

Then running clai will start an interactive session where you can chat with the AI model. Special commands available in interactive mode:

/exit: Exit the session
/markdown: Show the last response in markdown format
/multiline: Toggle multiline input mode (use Ctrl+D to submit)
/cp: Copy the last response to clipboard

CLI Options

Option	Description
`prompt`	AI prompt for one-shot mode (positional). If omitted, starts interactive mode.
`-m`, `--model`	Model to use in `provider:model` format (e.g., `openai:gpt-5.2`)
`-a`, `--agent`	Custom agent in `module:variable` format
`-t`, `--code-theme`	Syntax highlighting theme (`dark`, `light`, or pygments theme)
`--no-stream`	Disable streaming from the model
`-l`, `--list-models`	List all available models and exit
`--version`	Show version and exit

Choose a model

You can specify which model to use with the --model flag:

Terminal

clai --model anthropic:claude-sonnet-4-6

(a full list of models available can be printed with clai --list-models)

Custom Agents

You can specify a custom agent using the --agent flag with a module path and variable name:

custom_agent.py

from pydantic_ai import Agent

agent = Agent('openai:gpt-5.2', instructions='You always respond in Italian.')

Then run:

Terminal

clai --agent custom_agent:agent "What's the weather today?"

The format must be module:variable where:

module is the importable Python module path
variable is the name of the Agent instance in that module

Additionally, you can directly launch CLI mode from an Agent instance using Agent.to_cli_sync():

agent_to_cli_sync.py

from pydantic_ai import Agent

agent = Agent('openai:gpt-5.2', instructions='You always respond in Italian.')
agent.to_cli_sync()

You can also use the async interface with Agent.to_cli():

agent_to_cli.py

from pydantic_ai import Agent

agent = Agent('openai:gpt-5.2', instructions='You always respond in Italian.')

async def main():
    await agent.to_cli()

(You’ll need to add asyncio.run(main()) to run main)

Message History

Both Agent.to_cli() and Agent.to_cli_sync() support a message_history parameter, allowing you to continue an existing conversation or provide conversation context:

agent_with_history.py

from pydantic_ai import (
    Agent,
    ModelMessage,
    ModelRequest,
    ModelResponse,
    TextPart,
    UserPromptPart,
)

agent = Agent('openai:gpt-5.2')

# Create some conversation history
message_history: list[ModelMessage] = [
    ModelRequest([UserPromptPart(content='What is 2+2?')]),
    ModelResponse([TextPart(content='2+2 equals 4.')])
]

# Start CLI with existing conversation context
agent.to_cli_sync(message_history=message_history)

The CLI will start with the provided conversation history, allowing the agent to refer back to previous exchanges and maintain context throughout the session.

Web Chat UI

Launch a web-based chat interface by running:

Terminal

clai web -m openai:gpt-5.2

This will start a web server (default: http://127.0.0.1:7932) with a chat interface.

You can also serve an existing agent. For example, if you have an agent defined in my_agent.py:

from pydantic_ai import Agent

my_agent = Agent('openai:gpt-5.2', instructions='You are a helpful assistant.')

Launch the web UI:

Terminal

# With a custom agent
clai web --agent my_module:my_agent

# With specific models (first is default when no --agent)
clai web -m openai:gpt-5.2 -m anthropic:claude-sonnet-4-6

# With builtin tools
clai web -m openai:gpt-5.2 -t web_search -t code_execution

# Generic agent with system instructions
clai web -m openai:gpt-5.2 -i 'You are a helpful coding assistant'

# Custom agent with extra instructions for each run
clai web --agent my_module:my_agent -i 'Always respond in Spanish'

Web UI Options

Option	Description
`--agent`, `-a`	Agent to serve in `module:variable` format
`--model`, `-m`	Models to list as options in the UI (repeatable)
`--tool`, `-t`	Builtin tools to list as options in the UI (repeatable). See available tools.
`--instructions`, `-i`	System instructions. When `--agent` is specified, these are additional to the agent’s existing instructions.
`--host`	Host to bind server (default: 127.0.0.1)
`--port`	Port to bind server (default: 7932)
`--html-source`	URL or file path for the chat UI HTML.

When using --agent, the agent’s configured model becomes the default. CLI models (-m) are additional options. Without --agent, the first -m model is the default.

The web chat UI can also be launched programmatically using Agent.to_web(), see the Web UI documentation.

Run the web command with --help to see all available options:

Terminal

clai web --help