![ReDoc](https://fastapi.tiangolo.com/img/index/index-02-redoc-simple.png)

### OpenAPI

**FastAPI** generuje "schemat" z całym Twoim API przy użyciu standardu **OpenAPI** służącego do definiowania API.

#### Schema

"Schema" jest definicją lub opisem czegoś. Nie jest to kod, który go implementuje, ale po prostu abstrakcyjny opis.

    {!> ../../../docs_src/generate_clients/tutorial002_py39.py!}
    ```

=== "Python 3.8+"

    ```Python hl_lines="23  28  36"
    {!> ../../../docs_src/generate_clients/tutorial002.py!}
    ```

### Generate a TypeScript Client with Tags

If you generate a client for a FastAPI app using tags, it will normally also separate the client code based on the tags.

    new_field.populate_validators()  # type: ignore[attr-defined]
    return new_field


def generate_operation_id_for_path(
    *, name: str, path: str, method: str
) -> str:  # pragma: nocover
    warnings.warn(
        "fastapi.utils.generate_operation_id_for_path() was deprecated, "
        "it is not used internally, and will be removed soon",
        DeprecationWarning,

It's relatively tightly coupled with relational databases (like MySQL or PostgreSQL), so, having a NoSQL database (like Couchbase, MongoDB, Cassandra, etc) as the main store engine is not very easy.

It was created to generate the HTML in the backend, not to create APIs used by a modern frontend (like React, Vue.js and Angular) or by other systems (like <abbr title="Internet of Things">IoT</abbr> devices) communicating with it.

            """
        ),
    ] = ...,
    *,
    default_factory: Annotated[
        Union[Callable[[], Any], None],
        Doc(
            """
            A callable to generate the default value.

            This doesn't affect `Path` parameters as the value is always required.
            The parameter is available only for compatibility.
            """
        ),
    ] = _Unset,

And also after the `response` is generated, before returning it.

For example, you could add a custom header `X-Process-Time` containing the time in seconds that it took to process the request and generate a response:

```Python hl_lines="10  12-13"
{!../../../docs_src/middleware/tutorial001.py!}
```

## Other middlewares

Let's say you want to add translations for Creole, and it's not yet there in the docs.

Checking the link from above, the code for "Creole" is `ht`.

The next step is to run the script to generate a new translation directory:

<div class="termy">

```console
// Use the command new-lang, pass the language code as a CLI argument
$ python ./scripts/docs.py new-lang ht

For example:

```Python hl_lines="4-7"
{!../../../docs_src/behind_a_proxy/tutorial003.py!}
```

Will generate an OpenAPI schema like:

```JSON hl_lines="5-7"
{
    "openapi": "3.1.0",
    // More stuff here
    "servers": [
        {
            "url": "/api/v1"
        },
        {

And there are dozens of alternatives, all based on OpenAPI. You could easily add any of those alternatives to your application built with **FastAPI**.

You could also use it to generate code automatically, for clients that communicate with your API. For example, frontend, mobile or IoT applications.

## Recap, step by step

### Step 1: import `FastAPI`

```Python hl_lines="1"

async def dependency_a():
    dep_a = generate_dep_a()
    try:
        yield dep_a
    finally:
        dep_a.close()


async def dependency_b(dep_a=Depends(dependency_a)):
    dep_b = generate_dep_b()
    try:
        yield dep_b
    finally:
        dep_b.close(dep_a)


async def dependency_c(dep_b=Depends(dependency_b)):
    dep_c = generate_dep_c()
    try:
        yield dep_c
    finally: