oas-missing-type

All schemas and their properties should have a type field defined to ensure clarity about expected data types.

Why did this violation appear?

A schema or property is missing an explicit type definition. While OpenAPI/JSON Schema allows schemas without types, explicitly defining types improves API documentation clarity and helps prevent validation issues.

Bad example

Schema property without a type defined:

components:
  schemas:
    Pet:
      type: object
      properties:
        id:
          type: string
        name:
          description: "Name of the pet"
          # Missing type field - this will trigger a violation
        age:
          minimum: 0
          # Has constraints but no type - will trigger a violation

Good Example

All properties have explicit types:

components:
  schemas:
    Pet:
      type: object
      properties:
        id:
          type: string
        name:
          type: string
          description: "Name of the pet"
        age:
          type: integer
          minimum: 0

Exceptions

The following schemas don’t require explicit types:

1. Enum values - type can be inferred:

status:
  enum: ["active", "inactive"]  # Type inferred from values

2. Const values - type is implicit:

version:
  const: "1.0.0"  # Type is implicitly string

3. Polymorphic schemas - composed schemas don’t need their own type:

Pet:
  oneOf:
    - $ref: '#/components/schemas/Cat'
    - $ref: '#/components/schemas/Dog'

4. Schemas with structural properties - type can be inferred:

Address:
  properties:  # Implies type: object
    street:
      type: string

How do I fix this violation?

Add a type field to all schemas and properties. Valid types are:

• string
• number
• integer
• boolean
• array
• object
• null (OpenAPI 3.1 only)

For arrays, also define the items schema. For objects, define properties or use additionalProperties.