Let's see all this with an example.

Imagine you develop an app that allows creating invoices.

These invoices will have an `id`, `title` (optional), `customer`, and `total`.

The user of your API (an external developer) will create an invoice in your API with a POST request.

Then your API will (let's imagine):

* Send the invoice to some customer of the external developer.
* Collect the money.

from inline_snapshot import snapshot

app = FastAPI(
    servers=[
        {"url": "/", "description": "Default, relative server"},
        {
            "url": "http://staging.localhost.tiangolo.com:8000",
            "description": "Staging but actually localhost still",
        },
        {"url": "https://prod.example.com"},
    ]
)


@app.get("/foo")
def foo():
    return {"message": "Hello World"}

            {
                "item_id": "foo",
                "description": "This is an amazing item that has a long description",
            },
        ),
        (
            "/items/bar?q=somequery",
            {
                "item_id": "bar",
                "q": "somequery",
                "description": "This is an amazing item that has a long description",
            },
        ),
        (

                "owner_id": 123,
                "description": "This is an amazing item that has a long description",
            },
        ),
        (
            "/users/1/items/bar?q=somequery",
            {
                "item_id": "bar",
                "owner_id": 1,
                "q": "somequery",
                "description": "This is an amazing item that has a long description",
            },
        ),
        (

from fastapi import FastAPI, Request

app = FastAPI(
    servers=[
        {"url": "https://stag.example.com", "description": "Staging environment"},
        {"url": "https://prod.example.com", "description": "Production environment"},
    ],
    root_path="/api/v1",
)


@app.get("/app")
def read_main(request: Request):

from fastapi import FastAPI, Request

app = FastAPI(
    servers=[
        {"url": "https://stag.example.com", "description": "Staging environment"},
        {"url": "https://prod.example.com", "description": "Production environment"},
    ],
    root_path="/api/v1",
    root_path_in_servers=False,
)


@app.get("/app")
def read_main(request: Request):

):
    item = {"item_id": item_id, "owner_id": user_id}
    if q:
        item.update({"q": q})
    if not short:
        item.update(
            {"description": "This is an amazing item that has a long description"}
        )

            "servers": [
                {"url": "/api/v1"},
                {
                    "url": "https://stag.example.com",
                    "description": "Staging environment",
                },
                {
                    "url": "https://prod.example.com",
                    "description": "Production environment",
                },
            ],

@subrouter.post("/invoices/", callbacks=invoices_callback_router.routes)
def create_invoice(invoice: Invoice, callback_url: Optional[HttpUrl] = None):
    """
    Create an invoice.

    This will (let's imagine) let the API user (some external developer) create an
    invoice.

    And this path operation will:

    * Send the invoice to the client.
    * Collect the money from the client.

            "info": {"title": "FastAPI", "version": "0.1.0"},
            "servers": [
                {
                    "url": "https://stag.example.com",
                    "description": "Staging environment",
                },
                {
                    "url": "https://prod.example.com",
                    "description": "Production environment",
                },
            ],