Validation

A schema describes the shape of a value, and it can describe the range too. How long a name may be, that an amount is never negative, how few items an array may hold — mark these on the TypeSpec declaration and they reach the AsyncAPI document with everything else.

What maps to what

Each decorator becomes the draft-07 keyword of the same meaning. They target a property, a model, or a scalar declaration. On a scalar, every field that uses it carries the constraint — see Scalar.

TypeSpec decorator	Schema keyword
@minLength / @maxLength	minLength / maxLength
@pattern	pattern
@format	format
@minValue / @maxValue	minimum / maximum
@minValueExclusive / @maxValueExclusive	exclusiveMinimum / exclusiveMaximum
@minItems / @maxItems	minItems / maxItems

Example

model Product {
  @minLength(1) @maxLength(50) name: string;
  @minValue(0) @maxValueExclusive(1000000) price: float64;
  @minItems(1) @maxItems(10) tags: string[];
  @pattern("^[A-Z]{2}-\\d{4}$") sku: string;
  @format("uuid") id: string;
}

Product:
  type: object
  properties:
    name:
      type: string
      minLength: 1
      maxLength: 50
    price:
      type: number
      format: double
      minimum: 0
      exclusiveMaximum: 1000000
    tags:
      type: array
      items:
        type: string
      minItems: 1
      maxItems: 10
    sku:
      type: string
      pattern: ^[A-Z]{2}-\d{4}$
    id:
      type: string
      format: uuid
  required:
    - name
    - price
    - tags
    - sku
    - id

The keyword with no decorator

Nothing emits uniqueItems. @typespec/compiler has no decorator for it.

When a bound cannot be written

Two cases drop the keyword with a warning rather than emit a wrong value:

• the bound is not representable as a JSON number, such as @maxValue(9223372036854775807) on an int64
• it targets a date, time, or duration value

The codes are unrepresentable-numeric-constraint and unsupported-temporal-range-constraint.