JSON Schema Cheat Sheet
A reference for defining and validating JSON document structure using JSON Schema keywords, types, and constraints.
2 PagesIntermediateFeb 8, 2026
Basic Schema Structure
A minimal object schema with type and required fields.
json
{ "$schema": "https://json-schema.org/draft/2020-12/schema", "title": "Person", "type": "object", "properties": { "name": { "type": "string" }, "age": { "type": "integer", "minimum": 0 }, "email": { "type": "string", "format": "email" } }, "required": ["name", "age"], "additionalProperties": false}
String & Number Constraints
Common validation keywords for primitive types.
json
{ "username": { "type": "string", "minLength": 3, "maxLength": 20, "pattern": "^[a-zA-Z0-9_]+$" }, "price": { "type": "number", "minimum": 0, "exclusiveMaximum": 10000, "multipleOf": 0.01 }, "status": { "type": "string", "enum": ["active", "inactive", "pending"] }}
Arrays & Composition
Array validation and combining schemas.
json
{ "tags": { "type": "array", "items": { "type": "string" }, "minItems": 1, "uniqueItems": true }, "contact": { "oneOf": [ { "type": "string", "format": "email" }, { "type": "string", "format": "uri" } ] }, "discountedPrice": { "allOf": [ { "type": "number" }, { "minimum": 0 } ] }}
Key Keywords Reference
Frequently used JSON Schema keywords and what they do.
- type- Restricts value to one of: string, number, integer, boolean, object, array, null
- required- Array of property names that must be present on an object
- enum- Value must exactly match one of the listed values
- $ref- References another schema, e.g. `#/definitions/Address` or a `$defs` entry
- anyOf / oneOf / allOf- Value must match at least one, exactly one, or all listed subschemas
- additionalProperties- `false` disallows properties not listed in `properties`
- format- Semantic hint like `date-time`, `email`, `uri` (validated by some validators, advisory in others)
Pro Tip
Set `additionalProperties: false` on objects you fully control to catch typos in payloads early, but leave it open on schemas meant to be extended by consumers to avoid breaking forward compatibility.
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