Definicja schematu zawiera ścieżki API, możliwe parametry, które są przyjmowane przez endpointy, itp.

#### "Schemat" danych

Termin "schemat" może również odnosić się do wyglądu niektórych danych, takich jak zawartość JSON.

W takim przypadku będzie to oznaczać atrybuty JSON, ich typy danych itp.

#### OpenAPI i JSON Schema

                "application/json": {
                    "schema": {
                        "$ref": "#/components/schemas/HTTPValidationError"
                    }
                }
            }
        }
    }
}
```

The schemas are referenced to another place inside the OpenAPI schema:

```JSON hl_lines="4-16"
{
    "components": {
        "schemas": {
            "Message": {

* Generate <a href="https://json-schema.org" class="external-link" target="_blank">JSON Schema</a> definitions for your model, you can also use them anywhere else you like if it makes sense for your project.
* Those schemas will be part of the generated OpenAPI schema, and used by the automatic documentation <abbr title="User Interfaces">UIs</abbr>.

## Automatic docs

* Générer des définitions <a href="https://json-schema.org" class="external-link" target="_blank">JSON Schema</a> pour votre modèle, qui peuvent être utilisées où vous en avez besoin dans votre projet ensuite.
* Ces schémas participeront à la constitution du schéma généré OpenAPI, et seront donc utilisés par les documentations automatiquement générées.

## Documentation automatique

### Generate the OpenAPI schema

Then, use the same utility function to generate the OpenAPI schema, inside a `custom_openapi()` function:

{* ../../docs_src/extending_openapi/tutorial001.py hl[2,15:21] *}

### Modify the OpenAPI schema

Now you can add the ReDoc extension, adding a custom `x-logo` to the `info` "object" in the OpenAPI schema:

{* ../../docs_src/extending_openapi/tutorial001.py hl[22:24] *}

Então, o frontend (que roda no navegador) tentaria acessar `/openapi.json` e não conseguiria obter o OpenAPI schema.

Como temos um proxy com um prefixo de caminho de `/api/v1` para nossa aplicação, o frontend precisa buscar o OpenAPI schema em `/api/v1/openapi.json`.

```mermaid
graph LR

browser("Browser")

You can declare extra information in `Field`, `Query`, `Body`, etc. And it will be included in the generated JSON Schema.

You will learn more about adding extra information later in the docs, when learning to declare examples.

/// warning

Extra keys passed to `Field` will also be present in the resulting OpenAPI schema for your application.

So, the frontend (that runs in the browser) would try to reach `/openapi.json` and wouldn't be able to get the OpenAPI schema.

Because we have a proxy with a path prefix of `/api/v1` for our app, the frontend needs to fetch the OpenAPI schema at `/api/v1/openapi.json`.

```mermaid
graph LR

browser("Browser")

///

## OpenAPI and API docs

If you return additional status codes and responses directly, they won't be included in the OpenAPI schema (the API docs), because FastAPI doesn't have a way to know beforehand what you are going to return.

///

It will:

* Return that status code in the response.
* Document it as such in the OpenAPI schema (and so, in the user interfaces):

<img src="/img/tutorial/response-status-code/image01.png">

/// note

Some response codes (see the next section) indicate that the response does not have a body.