JSON Schema Cheat Sheet

Complete reference for Draft-07 and 2020-12 JSON Schema validation keywords

Basic Type Definitions

Specify acceptable data types for properties

StringMatches any UTF-8 string text

{ "type": "string" }

Number / IntegerFloating point or whole integer

{ "type": "number" }
{ "type": "integer" }

Booleantrue or false

{ "type": "boolean" }

NullMatches null value explicitly

{ "type": "null" }

Multiple Allowed TypesAllows either string or null

{ "type": ["string", "null"] }

Validate string length, regex patterns, and standard formats

Length limits

{ "type": "string", "minLength": 3, "maxLength": 50 }

Regex pattern match

{ "type": "string", "pattern": "^[a-z0-9_-]+$" }

Email format

{ "type": "string", "format": "email" }

URI / URL format

{ "type": "string", "format": "uri" }

Date-Time ISO 8601

{ "type": "string", "format": "date-time" }

UUID format

{ "type": "string", "format": "uuid" }

Boundary checking and divisibility

Range boundaries

{ "type": "number", "minimum": 0, "maximum": 100 }

Exclusive bounds

{ "type": "number", "exclusiveMinimum": 0 }

Multiple of stepMatches 5, 10, 15, 20...

{ "type": "number", "multipleOf": 5 }

Enforce required keys and forbid undeclared properties

Required fields

{ "type": "object", "required": ["id", "email"] }

Strict (No extra keys)

{ "type": "object", "additionalProperties": false }

Property count bounds

{ "type": "object", "minProperties": 1, "maxProperties": 10 }

Enforce list items and uniqueness

Uniform items

{ "type": "array", "items": { "type": "string" } }

Unique elements (Set)

{ "type": "array", "uniqueItems": true }

Array size range

{ "type": "array", "minItems": 1, "maxItems": 100 }

Combine multiple schema constraints

allOf (AND)

{ "allOf": [{ "$ref": "#/defs/User" }, { "required": ["role"] }] }

anyOf (OR)

{ "anyOf": [{ "type": "string" }, { "type": "number" }] }

oneOf (XOR)

{ "oneOf": [{ "required": ["email"] }, { "required": ["phone"] }] }

not (Invert)

{ "not": { "type": "string" } }