JSON Schema Examples

Minimal object

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "type": "object",
  "properties": {
    "name": { "type": "string" },
    "age":  { "type": "integer", "minimum": 0 }
  },
  "required": ["name"]
}

Enum / string pattern

{
  "type": "object",
  "properties": {
    "status": { "type": "string", "enum": ["active", "paused", "closed"] },
    "email":  { "type": "string", "format": "email" },
    "slug":   { "type": "string", "pattern": "^[a-z0-9-]+$" }
  }
}

Array of items

{
  "type": "array",
  "minItems": 1,
  "maxItems": 10,
  "uniqueItems": true,
  "items": {
    "type": "object",
    "properties": { "id": { "type": "integer" } },
    "required": ["id"]
  }
}

Nested objects with $ref

{
  "$defs": {
    "address": {
      "type": "object",
      "properties": {
        "street": { "type": "string" },
        "zip":    { "type": "string", "pattern": "^\\d{5}$" }
      }
    }
  },
  "type": "object",
  "properties": {
    "shipping": { "$ref": "#/$defs/address" },
    "billing":  { "$ref": "#/$defs/address" }
  }
}

oneOf — discriminated union

{
  "oneOf": [
    { "type": "object", "properties": { "kind": { "const": "dog" }, "bark": { "type": "string" } }, "required": ["kind","bark"] },
    { "type": "object", "properties": { "kind": { "const": "cat" }, "meow": { "type": "string" } }, "required": ["kind","meow"] }
  ]
}

Useful keywords

type

string | number | integer | boolean | null | array | object

required

Array of required property names

additionalProperties

false to reject unknown keys

minLength / maxLength

String constraints

minimum / maximum

Number constraints (exclusiveMinimum / exclusiveMaximum for open)

format

date-time, email, uri, uuid, ipv4, ipv6 (validator-specific)

allOf / anyOf / oneOf

Combinators

const

Match single value exactly