From Click - Milo

Click and Milo both use decorators, but they put the contract in different places. Click attaches CLI metadata through stacked decorators such as @click.option; Milo keeps the public contract in the Python signature, Annotated[...]metadata, defaults, and docstring.

Official references: Click commands and groups and Click arguments.

Before

import click


@click.group()
def cli():
    pass


@cli.command()
@click.option("--environment", required=True)
@click.option("--service", required=True)
@click.option("--version", default="latest")
def deploy(environment: str, service: str, version: str):
    click.echo({"environment": environment, "service": service, "version": version})

After

from typing import Annotated

from milo import CLI, Description, MinLen

cli = CLI(name="deployer", description="Deploy services")


@cli.command("deploy", description="Deploy a service")
def deploy(
    environment: Annotated[str, MinLen(1), Description("Target environment")],
    service: Annotated[str, MinLen(1), Description("Service name")],
    version: str = "latest",
) -> dict[str, str]:
    return {"environment": environment, "service": service, "version": version}


if __name__ == "__main__":
    cli.run()

Mapping

Click concept	Milo equivalent
`@click.command()`	`@cli.command("name", description="...")`
`@click.option("--name", default=...)`	`name: T = default`
`@click.option("--name", required=True)`	`name: T`
`@click.argument("name")`	Usually`name: T`; document any compatibility wrapper if argv shape must remain positional
`@click.group()`	`group = cli.group("name", description="...")`
`click.echo(...)`	Return structured values, or use`Context`output helpers
`click.Context` / `pass_context`	`ctx: Context = None`injection

Groups

from milo import CLI

cli = CLI(name="repo")
remote = cli.group("remote", description="Manage remotes")


@remote.command("list", description="List remotes")
def list_remotes() -> list[str]:
    return ["origin"]

CLI users run repo remote list. Programmatic and MCP callers use remote.list.

What To Watch

Click decorators can hide contract details above the function. In Milo, contract review starts at the function signature.
Avoid writing normal command output withprint() or click.echo()in code that may run under MCP. Return values are safer for agents and--format json.
If you rely on Click's exact positional argument behavior, migrate that command with a compatibility test before changing user-facing argv shape.