This also means that if something changed it will be **reflected** on the client code automatically. And if you **build** the client it will error out if you have any **mismatch** in the data used.

Когда вы создаёте свои API на основе FastAPI и допускаете в коде ошибку, то FastAPI обычно остановит её распространение внутри одного запроса, при обработке которого она возникла. 🛡

Клиент получит ошибку **500 Internal Server Error** в ответ на свой запрос, но приложение не сломается и будет продолжать работать с последующими запросами.

### Большие ошибки - Падение приложений

私たち人間は常に**間違い**を犯します。ソフトウェアには、ほとんど常に**バグ**があらゆる箇所に隠されています。🐛

### 小さなエラーは自動的に処理される

FastAPIでWeb APIを構築する際に、コードにエラーがある場合、FastAPIは通常、エラーを引き起こした単一のリクエストにエラーを含めます。🛡

クライアントはそのリクエストに対して**500 Internal Server Error**を受け取りますが、アプリケーションは完全にクラッシュするのではなく、次のリクエストのために動作を続けます。

### 重大なエラー - クラッシュ

しかしながら、**アプリケーション全体をクラッシュさせるようなコードを書いて**UvicornとPythonをクラッシュさせるようなケースもあるかもしれません。💥

### Small Errors Automatically Handled

When building web APIs with FastAPI, if there's an error in our code, FastAPI will normally contain it to the single request that triggered the error. 🛡

The client will get a **500 Internal Server Error** for that request, but the application will continue working for the next requests instead of just crashing completely.

### Bigger Errors - Crashes

<span style="color: green;">INFO</span>:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
```

</div>

Then if you go to the URLs at `/openapi.json`, `/docs`, or `/redoc` you will just get a `404 Not Found` error like:

```JSON
{
    "detail": "Not Found"
}

                    "schema": {
                        "$ref": "#/components/schemas/Item"
                    }
                }
            }
        },
        "422": {
            "description": "Validation Error",
            "content": {
                "application/json": {
                    "schema": {
                        "$ref": "#/components/schemas/HTTPValidationError"
                    }
                }

If it doesn't see an `Authorization` header, or the value doesn't have a `Bearer ` token, it will respond with a 401 status code error (`UNAUTHORIZED`) directly.

You don't even have to check if the token exists to return an error. You can be sure that if your function is executed, it will have a `str` in that token.

You can try it already in the interactive docs:

        dep -->> handler: Raise HTTPException
        handler -->> client: HTTP error response
        dep -->> dep: Raise other exception
    end
    dep ->> operation: Run dependency, e.g. DB session
    opt raise
        operation -->> dep: Raise HTTPException
        dep -->> handler: Auto forward exception
        handler -->> client: HTTP error response
        operation -->> dep: Raise other exception

```Python hl_lines="13  15"
{!../../../docs_src/custom_request_and_route/tutorial002.py!}
```

If an exception occurs, the`Request` instance will still be in scope, so we can read and make use of the request body when handling the error:

```Python hl_lines="16-18"
{!../../../docs_src/custom_request_and_route/tutorial002.py!}
```

## Custom `APIRoute` class in a router

You can also set the `route_class` parameter of an `APIRouter`:

```JSON
{
    "detail": [
        {
            "loc": [
                "query",
                "needy"
            ],
            "msg": "field required",
            "type": "value_error.missing"
        }
    ]
}
```

`needy` は必須のパラメータなので、URLにセットする必要があります:

```
http://127.0.0.1:8000/items/foo-item?needy=sooooneedy
```

...これはうまくいくでしょう:

```JSON
{