You put it on top of a function. Like a pretty decorative hat (I guess that's where the term came from).

A "decorator" takes the function below and does something with it.

In our case, this decorator tells **FastAPI** that the function below corresponds to the **path** `/` with an **operation** `get`.

It is the "**path operation decorator**".

///

You can also use the other operations:

* `@app.post()`

//// tab | `fastapi`

If you use the `fastapi` command:

<div class="termy">

```console
$ <pre> <font color="#4E9A06">fastapi</font> run --workers 4 <u style="text-decoration-style:single">main.py</u>
<font color="#3465A4">INFO    </font> Using path <font color="#3465A4">main.py</font>

#### Визначте декоратор операції шляху (path operation decorator)

```Python hl_lines="6"
{!../../docs_src/first_steps/tutorial001.py!}
```
Декоратор `@app.get("/")` вказує **FastAPI**, що функція нижче, відповідає за обробку запитів, які надходять до неї:

* шлях `/`
* використовуючи <abbr title="an HTTP GET method"><code>get</code> операцію</abbr>

/// info | "`@decorator` Додаткова інформація"

Link buttons\n//\n\n// Make a button look and behave like a link\n.btn-link {\n  font-weight: $font-weight-normal;\n  color: $link-color;\n  text-decoration: $link-decoration;\n\n  @include hover() {\n    color: $link-hover-color;\n    text-decoration: $link-hover-decoration;\n  }\n\n  &:focus,\n  &.focus {\n    text-decoration: $link-hover-decoration;\n  }\n\n  &:disabled,\n  &.disabled {\n    color: $btn-link-disabled-color;\n    pointer-events: none;\n  }\n\n  // No need for an active state here\n}\n\n\n//\n//...

gin-bottom:.5rem}p{margin-top:0;margin-bottom:1rem}abbr[data-original-title],abbr[title]{text-decoration:underline;-webkit-text-decoration:underline dotted;text-decoration:underline dotted;cursor:help;border-bottom:0;-webkit-text-decoration-skip-ink:none;text-decoration-skip-ink:none}address{margin-bottom:1rem;font-style:normal;line-height:inherit}dl,ol,ul{margin-top:0;margin-bottom:1rem}ol ol,ol ul,ul ol,ul ul{margin-bottom:0}dt{font-weight:700}dd{margin-bottom:.5rem;margin-left:0}blockquote{margin:0...

gin-bottom:.5rem}p{margin-top:0;margin-bottom:1rem}abbr[data-original-title],abbr[title]{text-decoration:underline;-webkit-text-decoration:underline dotted;text-decoration:underline dotted;cursor:help;border-bottom:0;-webkit-text-decoration-skip-ink:none;text-decoration-skip-ink:none}address{margin-bottom:1rem;font-style:normal;line-height:inherit}dl,ol,ul{margin-top:0;margin-bottom:1rem}ol ol,ol ul,ul ol,ul ul{margin-bottom:0}dt{font-weight:700}dd{margin-bottom:.5rem;margin-left:0}blockquote{margin:0...

To create the callback *path operation* use the same `APIRouter` you created above.

It should look just like a normal FastAPI *path operation*:

* It should probably have a declaration of the body it should receive, e.g. `body: InvoiceEvent`.
* And it could also have a declaration of the response it should return, e.g. `response_model=InvoiceEventReceived`.

```Python hl_lines="16-18  21-22  28-32"
{!../../docs_src/openapi_callbacks/tutorial001.py!}

**FastAPI** vous offre ceci:

### Basé sur des standards ouverts

FastAPI will use this `response_model` to do all the data documentation, validation, etc. and also to **convert and filter the output data** to its type declaration.

/// tip

If you have strict type checks in your editor, mypy, etc, you can declare the function return type as `Any`.

    response = client.get("/decorator-depends/?q=foo")
    assert response.status_code == 200
    assert response.json() == {"in": "decorator-depends"}


def test_decorator_depends_q_foo_skip_100_limit_200():
    response = client.get("/decorator-depends/?q=foo&skip=100&limit=200")
    assert response.status_code == 200
    assert response.json() == {"in": "decorator-depends"}


def test_router_depends():