no-enum-type-mismatch

Prevents an enum from containing values its schema type cannot represent.

Attribute	Value
Category	Schema
Maturity	Baseline
OpenAPI	Swagger 2.0; OpenAPI 3.0, 3.1, 3.2
Starter	Warning
Lenient	Error
Recommended	Error
Strict	Error
Complete	Error

Intent

An enum narrows a schema to named values. Each value must still satisfy the schema's declared type, or validators and generated clients receive contradictory instructions.

Flags

This rule reports each enum value that does not match type.

• A string enum cannot contain numbers or booleans.
• A number enum may contain integers or decimal numbers.
• OpenAPI 3.1/3.2 multi-value type accepts an enum value matching any declared type.
• A null enum value is accepted when OpenAPI 3.0 nullable: true applies.

Does not flag

• Schemas without both type and an array-valued enum.
• Enum values matching the declared type.
• A node containing $ref; referenced content is checked at its definition.

See it fail

openapi: 3.0.3
info:
  title: Pets API
  version: 1.0.0
paths: {}
components:
  schemas:
    PetType:
      type: string
      enum:
        - dog
        - 123

Specmatic points to the second enum value and reports:

All values of `enum` field must be of the same type as the `type` field: expected "string" but received "integer".

Fix it

Remove the mismatched value or express it using the declared type:

components:
  schemas:
    PetType:
      type: string
      enum:
        - dog
        - "123"

Configure

specmatic-linter.yaml

profiles:
  default:
    rules:
      extends:
        - recommended
      override:
        no-enum-type-mismatch: warn

Use error to block mismatched enums, warn during cleanup, or off to disable the rule.

Nearby rules

• no-schema-type-mismatch
• no-required-schema-properties-undefined
• oas30-enum-null-coercion