For development, prefer the command live (or just mkdocs serve).

    This is here only to preview a site with translations already built.

    Make sure you run the build-all command first.
    """
    typer.echo("Warning: this is a very simple server.")
    typer.echo("For development, use the command live instead.")

    "name": "Foo",
    "description": "The pretender",
    "price": 42.0,
    "tax": 3.2,
    "tags": ["rock", "metal", "bar"],
    "image": {
        "url": "http://example.com/baz.jpg",
        "name": "The Foo live"
    }
}
```

Again, doing just that declaration, with **FastAPI** you get:

* Editor support (completion, etc.), even for nested models
* Data conversion
* Data validation

Now, let's see the module at `app/main.py`.

Here's where you import and use the class `FastAPI`.

This will be the main file in your application that ties everything together.

And as most of your logic will now live in its own specific module, the main file will be quite simple.

### Import `FastAPI`

You import and create a `FastAPI` class as normally.

    "name": "Foo",
    "description": "The pretender",
    "price": 42.0,
    "tax": 3.2,
    "tags": ["rock", "metal", "bar"],
    "image": {
        "url": "http://example.com/baz.jpg",
        "name": "The Foo live"
    }
}
```

繰り返しになりますが、**FastAPI** を使用して、その宣言を行うだけで以下のような恩恵を受けられます:

* ネストされたモデルでも対応可能なエディタのサポート（補完など）
* データ変換
* データの検証
* 自動文書化

## 特殊な型とバリデーション

    "name": "Foo",
    "description": "The pretender",
    "price": 42.0,
    "tax": 3.2,
    "tags": ["rock", "metal", "bar"],
    "image": {
        "url": "http://example.com/baz.jpg",
        "name": "The Foo live"
    }
}
```

再一次，仅仅进行这样的声明，你将通过 **FastAPI** 获得：

* 对被嵌入的模型也适用的编辑器支持（自动补全等）
* 数据转换
* 数据校验
* 自动生成文档

## 特殊的类型和校验

    "name": "Foo",
    "description": "The pretender",
    "price": 42.0,
    "tax": 3.2,
    "tags": ["rock", "metal", "bar"],
    "image": {
        "url": "http://example.com/baz.jpg",
        "name": "The Foo live"
    }
}
```

🔄, 🤸 👈 📄, ⏮️ **FastAPI** 👆 🤚:

* 👨‍🎨 🐕‍🦺 (🛠️, ♒️), 🐦 🏷
* 💽 🛠️
* 💽 🔬
* 🏧 🧾

## 🎁 🆎 & 🔬

    !!! tip
        Prefer to use the `Annotated` version if possible.

    ```Python hl_lines="10"
    {!> ../../../docs_src/security/tutorial001.py!}
    ```

But that is still not that useful.

Let's make it give us the current user.

## Create a user model

First, let's create a Pydantic user model.

The same way we use Pydantic to declare bodies, we can use it anywhere else:

=== "Python 3.10+"

```Python hl_lines="7"
{!../../../docs_src/path_params/tutorial002.py!}
```

In this case, `item_id` is declared to be an `int`.

!!! check
    This will give you editor support inside of your function, with error checks, completion, etc.

## Data <abbr title="also known as: serialization, parsing, marshalling">conversion</abbr>

### Internal

* 🔨 Enable linenums in MkDocs Material during local live development to simplify highlighting code. PR [#9769](https://github.com/tiangolo/fastapi/pull/9769) by [@tiangolo](https://github.com/tiangolo).

I'll tell you a bit more about these **concepts** here, and that would hopefully give you the **intuition** you would need to decide how to deploy your API in very different environments, possibly even in **future** ones that don't exist yet.

By considering these concepts, you will be able to **evaluate and design** the best way to deploy **your own APIs**.

In the next chapters, I'll give you more **concrete recipes** to deploy FastAPI applications.