YAML Schema String Type Constraints from JSON

String Type Mapping in YAML Schema

JSON string values map to type: string in YAML Schema. Beyond basic type assertion, YAML Schema offers rich constraints that let you validate string content precisely.

Basic String Property

{
  "name": "my-service",
  "email": "admin@example.com",
  "version": "2.1.0"
}

type: object
properties:
  name:
    type: string
  email:
    type: string
    format: email
  version:
    type: string
    pattern: "^\\d+\\.\\d+\\.\\d+$"

String Constraints

Constraint	Purpose	Example
minLength	Minimum character count	minLength: 1 (non-empty)
maxLength	Maximum character count	maxLength: 255
pattern	Regex the value must match	pattern: "^[a-z0-9-]+$"
format	Semantic format hint	format: email
enum	Fixed set of allowed values	enum: ["info", "warn", "error"]
default	Default value when absent	default: "info"

Format Keywords

The format keyword provides semantic validation beyond regex:

properties:
  email:
    type: string
    format: email
  homepage:
    type: string
    format: uri
  createdAt:
    type: string
    format: date-time
  ip:
    type: string
    format: ipv4

Common formats: date-time, date, time, email, uri, hostname, ipv4, ipv6, uuid.

Pattern Validation

Use pattern for custom validation rules:

properties:
  slug:
    type: string
    pattern: "^[a-z0-9]+(-[a-z0-9]+)*$"
    description: URL-safe slug (lowercase, hyphens only)
  semver:
    type: string
    pattern: "^\\d+\\.\\d+\\.\\d+(-[a-zA-Z0-9.]+)?$"
    description: Semantic version string

Content Encoding

For binary data stored as strings:

certificate:
  type: string
  contentEncoding: base64
  contentMediaType: application/x-pem-file

Smart Inference

An intelligent converter detects common string patterns and automatically applies appropriate constraints -- email addresses get format: email, ISO dates get format: date-time, and URL strings get format: uri.