YAML Schema Boolean and Null Types from JSON

Boolean and Null Type Mapping

JSON true/false values map to type: boolean in YAML Schema. JSON null introduces nullable types, which require special handling in the schema definition.

Boolean Properties

{
  "debug": true,
  "enableCache": false,
  "verbose": true
}

type: object
properties:
  debug:
    type: boolean
    default: false
  enableCache:
    type: boolean
    default: true
  verbose:
    type: boolean
    default: false

Nullable Properties

When a JSON field is null, the schema must allow the null type alongside the expected type:

{
  "name": "Alice",
  "nickname": null,
  "age": 30,
  "bio": null
}

type: object
properties:
  name:
    type: string
  nickname:
    type:
      - string
      - "null"
  age:
    type: integer
  bio:
    type:
      - string
      - "null"

Draft 2020-12 Nullable Syntax

In JSON Schema draft 2020-12, nullable types use an array syntax:

nickname:
  type: [string, "null"]

In earlier drafts, you use oneOf:

nickname:
  oneOf:
    - type: string
    - type: "null"

YAML Boolean Pitfall

YAML parsers interpret several values as boolean: yes, no, on, off, true, false. In YAML Schema definitions, always quote "null" to prevent the parser from interpreting it as a special value:

# Correct
type: [string, "null"]

# Dangerous -- YAML may parse null as empty
type: [string, null]

Boolean with Description

Adding descriptions to boolean fields improves schema usability:

debug:
  type: boolean
  default: false
  description: >
    Enable debug mode. When true, the application logs
    detailed request/response bodies and stack traces.

Combining Boolean with Conditional Logic

properties:
  tls:
    type: boolean
  certPath:
    type: string
if:
  properties:
    tls:
      const: true
then:
  required:
    - certPath

This schema makes certPath required only when tls is true, enabling conditional validation based on boolean flags.