You should also define a default response schema for your operations as a catch-all for undeclared specific return codes. This will help your users know what to do with unspecified HTTP return codes.

Noncompliant Code Example

openapi: "3.0.1"
info:
  version: 1.0.0
  title: Swagger Petstore
paths:
  /pets:
    get:
      # No default response defined
      responses:
        '200':
          description: list correctly retrieved
          content: {
            # content definition skipped
          }

Compliant Solution

openapi: "3.0.1"
info:
  version: 1.0.0
  title: Swagger Petstore
paths:
  /pets:
    get:
      responses:
        default:
          $ref: '#/responses/ErrorResponse'
        '200':
          description: list correctly retrieved
          content: {
            # content definition skipped
          }
responses:
  ErrorResponse:
    description: Default error response of the API
    content: {
      # content definition skipped
    }