# Parámetros de Header { #header-parameters }

Puedes definir los parámetros de Header de la misma manera que defines los parámetros de `Query`, `Path` y `Cookie`.

## Importar `Header` { #import-header }

Primero importa `Header`:

{* ../../docs_src/header_params/tutorial001_an_py310.py hl[3] *}

## Declarar parámetros de `Header` { #declare-header-parameters }

Si tienes un grupo de **parámetros de header** relacionados, puedes crear un **modelo Pydantic** para declararlos.

Esto te permitirá **reutilizar el modelo** en **múltiples lugares** y también declarar validaciones y metadatos para todos los parámetros al mismo tiempo. 😎

/// note | Nota

Esto es compatible desde la versión `0.115.0` de FastAPI. 🤓

///

///

## Benutzerdefinierte Header { #custom-headers }

Beachten Sie, dass benutzerdefinierte proprietäre Header <a href="https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers" class="external-link" target="_blank">mittels des Präfix `X-`</a> hinzugefügt werden können.

def test_header_repr_str():
    assert repr(Header("teststr")) == "Header(teststr)"


def test_header_repr_none():
    assert repr(Header(None)) == "Header(None)"


def test_header_repr_ellipsis():
    assert repr(Header(...)) == "Header(PydanticUndefined)"


def test_header_repr_number():
    assert repr(Header(1)) == "Header(1)"


def test_header_repr_list():

from fastapi import FastAPI, Header
from fastapi.testclient import TestClient
from pydantic import BaseModel, Field

app = FastAPI()

# =====================================================================================
# Without aliases


@app.get("/required-str")
async def read_required_str(p: Annotated[str, Header()]):
    return {"p": p}


class HeaderModelRequiredStr(BaseModel):

import pytest
from fastapi import FastAPI, Header
from fastapi.testclient import TestClient
from pydantic import BaseModel, Field

app = FastAPI()

# =====================================================================================
# Without aliases


@app.get("/optional-list-str")
async def read_optional_list_str(
    p: Annotated[Optional[list[str]], Header()] = None,
):
    return {"p": p}

import pytest
from fastapi import FastAPI, Header
from fastapi.testclient import TestClient
from pydantic import BaseModel, Field

app = FastAPI()

# =====================================================================================
# Without aliases


@app.get("/optional-str")
async def read_optional_str(p: Annotated[Optional[str], Header()] = None):
    return {"p": p}

from fastapi import FastAPI, Header
from fastapi.testclient import TestClient
from pydantic import BaseModel, Field

app = FastAPI()

# =====================================================================================
# Without aliases


@app.get("/required-list-str")
async def read_required_list_str(p: Annotated[list[str], Header()]):
    return {"p": p}

                                "in": "header",
                                "required": True,
                                "schema": {"type": "string", "title": "Host"},
                            },
                            {
                                "name": "save-data",
                                "in": "header",
                                "required": True,

    assert response.json() == {
        "detail": [
            {
                "type": "missing",
                "loc": ["header", "x-token"],
                "msg": "Field required",
                "input": None,
            },
            {
                "type": "missing",
                "loc": ["header", "x-key"],
                "msg": "Field required",
                "input": None,
            },
        ]
    }