Introduction to JSON Schema

JSON Schema is a vocabulary that lets you annotate and validate JSON documents. Think of it as a type system for JSON — you describe the shape of valid data, and validators check that documents conform to it.

Why Use JSON Schema?

• ·Validate API request/response payloads
• ·Document the expected shape of your data
• ·Generate forms, TypeScript types, and documentation automatically
• ·Catch data quality issues early in data pipelines

Basic Types

Every schema has a "type" keyword. JSON Schema supports: string, number, integer, boolean, null, object, and array.

{
  "type": "object",
  "properties": {
    "name":  { "type": "string" },
    "age":   { "type": "integer", "minimum": 0 },
    "email": { "type": "string", "format": "email" },
    "active": { "type": "boolean" }
  },
  "required": ["name", "email"]
}

String Constraints

• ·minLength / maxLength — character count bounds
• ·pattern — validates against a regex: "pattern": "^[A-Z]{2}[0-9]{6}
  quot;
• ·format — semantic validation: "email", "date-time", "uri", "uuid"
• ·enum — restrict to specific values: "enum": ["draft", "published", "archived"]

Object Validation

{
  "type": "object",
  "properties": {
    "status": { "enum": ["active", "inactive"] }
  },
  "required": ["status"],
  "additionalProperties": false
}

Setting "additionalProperties": false makes the schema strict — any field not listed in "properties" will fail validation. This is great for catching typos in field names.

Array Validation

{
  "type": "array",
  "items": { "type": "string" },
  "minItems": 1,
  "maxItems": 10,
  "uniqueItems": true
}

Combining Schemas

JSON Schema provides keywords to combine schemas logically.

• ·allOf — must be valid against ALL sub-schemas (like intersection)
• ·anyOf — must be valid against AT LEAST ONE sub-schema (like union)
• ·oneOf — must be valid against EXACTLY ONE sub-schema
• ·not — must NOT be valid against the sub-schema