JSON Schema

In more detail

JSON Schema is a vocabulary, written in JSON itself, for describing what valid JSON data looks like. A schema lists the expected types, required properties, allowed values and limits, and a validator checks a document against it and reports every mismatch.

The core keywords are type, properties, required, items, enum and const, plus limits such as minimum, maxLength and pattern. $ref reuses a definition, and oneOf, anyOf and allOf combine schemas.

The specification has several drafts. Draft 2020-12 is the current one and is what OpenAPI 3.1 uses. The $schema keyword at the top says which draft a schema follows.

Teams use JSON Schema to validate API requests and config files, generate types and forms, and document data formats. You can generate a first schema from a sample document and tighten it by hand.

Example

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "type": "object",
  "required": ["id", "email"],
  "properties": {
    "id": { "type": "integer", "minimum": 1 },
    "email": { "type": "string", "format": "email" },
    "role": { "enum": ["admin", "editor", "viewer"] }
  }
}

Try it