REST Lens

Category: Status Codes & Responses

Description

Responses with body content and request bodies must specify a Content-Type media type. Empty content definitions indicate missing type information.

What It Checks

This rule validates:

Response content definitions are not empty for 2XX, 4XX, and 5XX responses
Request body content definitions are not empty
Excludes 204 and 304 responses (which shouldn't have bodies)

Why It Matters

Specifying Content-Type is essential for:

Interoperability: Clients know how to parse responses
Documentation: Clear contract about data formats
Tooling Support: Code generators need content type information
HTTP Compliance: Content-Type is required for message bodies

Examples

Good

paths:
  /users:
    get:
      operationId: getUsers
      responses:
        '200':
          description: List of users
          content:
            application/json:
              schema:
                type: array
    post:
      operationId: createUser
      requestBody:
        content:
          application/json:
            schema:
              type: object
      responses:
        '201':
          description: User created
          content:
            application/json:
              schema:
                type: object

Bad

paths:
  /users:
    post:
      operationId: createUser
      requestBody:
        content: {}  # Empty content definition
      responses:
        '200':
          description: Success
          content: {}  # Empty content definition

Exceptions

204 No Content responses (should not have a body)
304 Not Modified responses (should not have a body)
Responses that legitimately have no body

Configuration

This rule has no configuration options. It is either enabled or disabled.

Related Rules

Rule 35: Code 204 Empty - No content responses
Rule 41: Consistent Media Types - Media type consistency
Rule 10: 415 Unsupported Media Type - Content type errors

Content-Type Must Be Used