Have you ever designed an API using OpenAPI or Swagger?

Yes, I have had to design APIs using OpenAPI (formerly known as Swagger). OpenAPI allows for a formal description of the REST API structure, including paths, methods, parameters, data schemas, and responses. This facilitates communication between teams, automatic documentation generation, and even client SDKs.

An example of describing a simple GET request in OpenAPI (YAML):

paths:
  /users:
    get:
      summary: Get a list of users
      responses:
        '200':
          description: Successful response
          content:
            application/json:
              schema:
                type: array
                items:
                  $ref: '#/components/schemas/User'
components:
  schemas:
    User:
      type: object
      properties:
        id:
          type: integer
        name:
          type: string

This approach helps clearly define the API contract and simplifies further development and testing.