Parameters are used to describe inputs to an operation. Parameters can be defined at the path or operation level and are merged with any duplicates at the operation level, overriding any defined at the path level.

Each parameter needs to be uniquely identified by a combination of its name and in fields in an operation.

A parameter in the list can either be a Parameter Object or a Reference to a Parameter Object defined in the Components Object under the parameters field.

Parameters can represent a number of different input types, including:

  • Path Parameters
  • Query Parameters
  • Headers
  • Cookies


- name: type
in: path
description: The type of drink to filter by.
required: true
$ref: "#/components/schemas/DrinkType"
- name: Cache-Control
in: header
description: The cache control header.
required: false
type: string
- no-cache
- no-store
- must-revalidate
- max-age=0
- max-age=3600
- max-age=86400
- max-age=604800
- max-age=2592000
- max-age=31536000
operationId: listDrinks
summary: Get a list of drinks.
description: Get a list of drinks, if authenticated this will include stock levels and product codes otherwise it will only include public information.
- {}
- drinks
- name: limit
in: query
description: The maximum number of drinks to return.
required: false
type: integer
minimum: 1
maximum: 100
description: A list of drinks.
type: array
$ref: "#/components/schemas/Drink"

Parameter Object

nameStringThe case sensitive name of the parameter. This must be unique when combined with the in field.

If the in field is path, then this field must be referenced in the owning path.
inStringThe type or location of the parameter. The available types are:
  • path - A templated parameter defined within the path.
  • query - A query parameter passed via the URL.
  • header - A header parameter passed via HTTP headers.
  • cookie - A cookie parameter passed via HTTP cookies.
descriptionStringA description of the parameter. This may contain CommonMark syntax (opens in a new tab) to provide a rich description.
requiredBooleanWhether the parameter is required. If the in field is path, then this field is always required and must be true. Defaults to false.
deprecatedBooleanWhether the parameter is deprecated. Defaults to false.
styleStringDescribes how the parameter value will be serialized depending on the in field. The available styles are matrix, label, form, simple, spaceDelimited, pipeDelimited, and deepObject.

The default style depends on the in field:
  • path - simple
  • query - form
  • header - simple
  • cookie - form
See the path (opens in a new tab), header (opens in a new tab), query (opens in a new tab), and cookie (opens in a new tab) parameter sections for more details.
explodeBooleanWhether the parameter value will be exploded, based on the parameter type. Defaults to true when style is form, otherwise false.

See the path (opens in a new tab), header (opens in a new tab), query (opens in a new tab), and cookie (opens in a new tab) parameter sections for more details.
schemaSchema ObjectA schema or reference to a schema that defines the type of the parameter. This is required unless content is defined.

Note: OpenAPI 3.0.x supports OpenAPI Reference Objects here as the value. OpenAPI 3.1.x uses the JSON Schema Referencing format.
contentContentA map of Media Type Objects that defines the possible media types that can be used for the parameter. This is required unless schema is defined.
allowEmptyValueBooleanWhether the parameter value can be empty. Only used if in is query. Defaults to false.
allowReservedBooleanWhether the parameter value can contain reserved characters as defined by RFC 3986 (opens in a new tab). Only used if in is query. Defaults to false.
exampleAnyAn example of the parameter's value. This is ignored if the examples field is defined.
examples[Examples])examples)A map of Example Objects and/or OpenAPI Reference Objects that define the possible examples of the parameter's value.
x-*ExtensionsAny number of extension fields can be added to the parameter object that can be used by tooling and vendors.

The order of fields above is recommended for defining fields in the document.

Parameter Serialization

Depending on the parameter's in, style, and explode fields and schema type, the parameter value will be serialized in different ways. Some combinations of schema type and parameter serialization are not valid and should be avoided.

The content field can be used instead to define complex serialization scenarios for a parameter such as serializing an object to a JSON string for including in a query parameter in the URL.