content-type-header-declared

Disallows declaring Content-Type as an OpenAPI header parameter or response header.

Attribute	Value
Category	Operations
Maturity	Platinum
OpenAPI	Swagger 2.0; OpenAPI 3.0, 3.1, 3.2
Starter	Off
Lenient–Strict	Warning
Complete	Error

Intent

OpenAPI represents media types through request-body and response content maps. A separate Content-Type declaration duplicates that information and can contradict it.

Flags

• A path-level or operation-level header parameter named Content-Type.
• A response header named Content-Type.

Names are matched case-insensitively.

Does not flag

Other headers or media types declared as keys under content.

See it fail

parameters:
  - name: Content-Type
    in: header
    schema:
      type: string

Diagnostic: Content-Type should not be declared as a header per OAS standards

Fix it

Remove the header parameter and declare the request media type on the body:

requestBody:
  content:
    application/json:
      schema:
        type: object

Configure

profiles:
  default:
    rules:
      extends: [recommended]
      override:
        content-type-header-declared: error

:::caution Policy overlap

content-type-response and header-required-for-content-type-response require this response header in some situations. Do not enable those rules together with this rule; choose the media-type policy your API follows and turn the conflicting rules off.

:::

Nearby: content-type-header-overrides-media-type, request-mime-type, response-mime-type.