app = FastAPI()


@app.get("/items/{item_id}")
def main(
    item_id: int = Path(default=..., gt=0),
    query: str = Query(default=..., max_length=10),
    session: str = Cookie(default=..., min_length=3),
    x_trace: str = Header(default=..., title="Tracing header"),
):
    return {"message": "Hello World"}
```

**Spoiler alert**: the tutorial - user guide includes:

* Declaration of **parameters** from other different places as: **headers**, **cookies**, **form fields** and **files**.
* How to set **validation constraints** as `maximum_length` or `regex`.
* A very powerful and easy to use **<abbr title="also known as components, resources, providers, services, injectables">Dependency Injection</abbr>** system.

**Spoiler alert**: the tutorial - user guide includes:

* Declaration of **parameters** from other different places as: **headers**, **cookies**, **form fields** and **files**.
* How to set **validation constraints** as `maximum_length` or `regex`.
* A very powerful and easy to use **<abbr title="also known as components, resources, providers, services, injectables">Dependency Injection</abbr>** system.