This document collects short explanations of terminology one may encounter within the JSON Schema community.

Whilst many of the entries below have precise technical definitions, preference is given to explanations of their conversational use, with additional references linked for further information. This page is not meant to be normative, nor is it meant to contain fully original research or explanation. It is meant to aid the understanding of those less familiar with formal language used within JSON Schema, or within specifications more broadly. (In fact, entries below make effort to avoid terminology like “normative” itself for reasons just mentioned.)

If you encounter a term you wish were defined here, please feel free to file an issue requesting it.

The entries on this page can be linked to via anchor links (e.g. https://json-schema.org/learn/glossary.html#vocabulary) when sharing a definition with others.

draft #

An individual release of the JSON Schema specification.

JSON Schema drafts are not intended to be provisional documents, as the layman’s use of the word “draft” might indicate.

While future drafts may introduce new behavior or changes to existing behavior, each draft is a completed, released document, batching together changes to the specification, and intended for implementation and use.

The current list of drafts can be found here.

keyword #

A property appearing within a schema object.

The JSON Schema specification defines behavior for a large library of keywords which can be used to describe instances.

instance #

A piece of JSON data which is to be described by a schema.

JSON Schema can be used to describe JSON values of any type (as well as values from many JSON-like formats which can be reasonably represented as JSON).

The JSON Schema specification makes no broad assumptions about the structure of instances themselves beyond those of the JSON specification itself. In particular it does not reserve any properties within a JSON object for its own use, or require parsers of JSON to support features beyond those already mandated of JSON implementations.

meta-schema #

A schema which is itself intended to describe other schemas.

JSON Schema defines a language for describing any instance using a schema written in JSON. Since schemas are themselves JSON values, they may be also be treated as instances, and therefore described by other schemas.

We refer to the schema-of-a-schema as a “meta-schema” to express this use.

normative #

In the context of JSON Schema, and formal specifications more broadly, a document which outlines standardized behavior. This is as distinct from non-normative or informational documents, meant to explain, simplify or offer opinions.

Distinguishing between whether a document is normative or not is intended to clarify to those using the document whether its contents are allowed to contradict or augment behavior described in other normative documents. JSON Schema’s normative documents notably include its specification. This page for instance, not being a normative document, is not able to proscribe new JSON Schema behavior not already covered by the specification.

See also #

schema #

A document, written according to the proscribed structure of the JSON Schema specification, which can be used to describe instances.

The rules constituting which schemas are conformant, as well as the rules governing their behavior when validating instances, are defined by the JSON Schema specification.

Strictly speaking, according to the specification, schemas are themselves JSON documents, though it is somewhat common for them to be authored or maintained in other languages which are easily translated to JSON, such as YAML.

In recent drafts of the specification, a schema is either a JSON object or a JSON boolean value.