Header

This class defines a parameter to be extracted from HTTP request headers, supporting validation, documentation, and metadata configuration. It extends the base parameter functionality with specific support for automatic underscore-to-hyphen conversion and OpenAPI schema integration. Users can specify constraints such as length, patterns, and default values for header-based data extraction.

Attributes

Attribute	Type	Description
in_	[ParamTypes](paramtypes.md?sid=fastapi_params_paramtypes) = ParamTypes.header	The location of the parameter in the request, which is fixed to the header for this class.
convert_underscores	bool = True	Whether to automatically convert underscores in the attribute name to hyphens when looking up the header value.

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Constructor

Signature

def Header(
    default: Any = Undefined,
    default_factory: Callable[[], Any]| None = _Unset,
    annotation: Any | None = None,
    alias: str | None = None,
    alias_priority: int | None = _Unset,
    validation_alias: str | AliasPath | AliasChoices | None = None,
    serialization_alias: str | None = None,
    convert_underscores: bool = True,
    title: str | None = None,
    description: str | None = None,
    gt: float | None = None,
    ge: float | None = None,
    lt: float | None = None,
    le: float | None = None,
    min_length: int | None = None,
    max_length: int | None = None,
    pattern: str | None = None,
    regex: str | None = None,
    discriminator: str | None = None,
    strict: bool | None = _Unset,
    multiple_of: float | None = _Unset,
    allow_inf_nan: bool | None = _Unset,
    max_digits: int | None = _Unset,
    decimal_places: int | None = _Unset,
    examples: list[Any]| None = None,
    example: Any | None = _Unset,
    openapi_examples: dict[str, [Example](../openapi/models/example.md?sid=fastapi_openapi_models_example)]| None = None,
    deprecated: deprecated | str | bool | None = None,
    include_in_schema: bool = True,
    json_schema_extra: dict[str, Any]| None = None,
    **extra: Any
) - > null

Parameters

Name	Type	Description
default	Any = Undefined	The default value for the header.
default_factory	`Callable[[], Any]	None` = _Unset
annotation	`Any	None` = None
alias	`str	None` = None
alias_priority	`int	None` = _Unset
validation_alias	`str	AliasPath
serialization_alias	`str	None` = None
convert_underscores	bool = True	Whether to automatically convert underscores to hyphens in the header name.
title	`str	None` = None
description	`str	None` = None
gt	`float	None` = None
ge	`float	None` = None
lt	`float	None` = None
le	`float	None` = None
min_length	`int	None` = None
max_length	`int	None` = None
pattern	`str	None` = None
regex	`str	None` = None
discriminator	`str	None` = None
strict	`bool	None` = _Unset
multiple_of	`float	None` = _Unset
allow_inf_nan	`bool	None` = _Unset
max_digits	`int	None` = _Unset
decimal_places	`int	None` = _Unset
examples	`list[Any]	None` = None
example	`Any	None` = _Unset
openapi_examples	`dict[str, Example]	None` = None
deprecated	`deprecated	str
include_in_schema	bool = True	Whether to include this parameter in the generated OpenAPI schema.
json_schema_extra	`dict[str, Any]	None` = None
**extra	Any	Additional keyword arguments.

---

Signature

def Header(
    default: Any = Undefined,
    default_factory: Callable[[], Any]| None = _Unset,
    annotation: Any | None = None,
    alias: str | None = None,
    alias_priority: int | None = _Unset,
    validation_alias: str | AliasPath | AliasChoices | None = None,
    serialization_alias: str | None = None,
    convert_underscores: bool = True,
    title: str | None = None,
    description: str | None = None,
    gt: float | None = None,
    ge: float | None = None,
    lt: float | None = None,
    le: float | None = None,
    min_length: int | None = None,
    max_length: int | None = None,
    pattern: str | None = None,
    regex: str | None = None,
    discriminator: str | None = None,
    strict: bool | None = _Unset,
    multiple_of: float | None = _Unset,
    allow_inf_nan: bool | None = _Unset,
    max_digits: int | None = _Unset,
    decimal_places: int | None = _Unset,
    examples: list[Any]| None = None,
    example: Any | None = _Unset,
    openapi_examples: dict[str, [Example](../openapi/models/example.md?sid=fastapi_openapi_models_example)]| None = None,
    deprecated: deprecated | str | bool | None = None,
    include_in_schema: bool = True,
    json_schema_extra: dict[str, Any]| None = None,
    extra: Any
) - > null

Parameters

Name	Type	Description
default	Any = Undefined	The default value for the header if it is not provided in the request.
default_factory	`Callable[[], Any]	None` = _Unset
annotation	`Any	None` = None
alias	`str	None` = None
alias_priority	`int	None` = _Unset
validation_alias	`str	AliasPath
serialization_alias	`str	None` = None
convert_underscores	bool = True	Whether to automatically convert underscores in the parameter name to hyphens (e.g., user_agent to User-Agent).
title	`str	None` = None
description	`str	None` = None
gt	`float	None` = None
ge	`float	None` = None
lt	`float	None` = None
le	`float	None` = None
min_length	`int	None` = None
max_length	`int	None` = None
pattern	`str	None` = None
regex	`str	None` = None
discriminator	`str	None` = None
strict	`bool	None` = _Unset
multiple_of	`float	None` = _Unset
allow_inf_nan	`bool	None` = _Unset
max_digits	`int	None` = _Unset
decimal_places	`int	None` = _Unset
examples	`list[Any]	None` = None
example	`Any	None` = _Unset
openapi_examples	`dict[str, Example]	None` = None
deprecated	`deprecated	str
include_in_schema	bool = True	Whether this header should be visible in the generated OpenAPI schema.
json_schema_extra	`dict[str, Any]	None` = None
extra	Any	Additional keyword arguments passed to the underlying Pydantic model.

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