string-schema-format-required

Requires unconstrained string properties and parameters to declare a format.

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

Intent

A format gives generic strings useful domain meaning, improving generated examples, validation, and client types.

Flags

• Direct string properties of component schemas with neither format nor a non-empty enum.
• String schemas on query, path, header, or cookie parameters with neither format nor a non-empty enum.

Nested component properties and body-only inline strings are not checked.

See it fail

components:
  schemas:
    Customer:
      type: object
      properties:
        email:
          type: string

Diagnostic: String properties should define a format.

Fix it

email:
  type: string
  format: email

An enum also satisfies the rule:

status:
  type: string
  enum: [active, inactive]

Configure

profiles:
  default:
    rules:
      extends: [recommended]
      override:
        string-schema-format-required: error

Nearby: string-parameter-pattern-required, string-max-length-or-enum.