api: YAML JSON TOON Database
version: 1.0.0
format: json
dataset:
  id: 1005
  slug: json-schema-keywords
  title: JSON Schema 2020-12 Keyword Reference
  description: "Core validation and composition keywords in JSON Schema 2020-12, with compact examples and traps."
  summary: "Core validation and composition keywords in JSON Schema 2020-12, with compact examples and traps. Each row includes a practical application and a failure to check before using it."
  use_when[2]: Validate a dataset before sending it to an agent.,Design a small contract for API input or a downloaded table.
  caveats[2]: These examples target draft 2020-12.,Validation does not establish factual correctness.
  related[2]: date-time-interchange,http-response-headers
  category: Web Technologies
  category_slug: web-technologies
  tags: "web-technologies,json schema keywords,reference,engineering"
  view_count: 0
  created_at: 1791798640
  updated_at: 1791798640
  reviewed_at: 2026-10-12
  sources[2]{title,url}:
    JSON Schema validation specification,"https://json-schema.org/draft/2020-12/json-schema-validation"
    JSON Schema reference,"https://json-schema.org/understanding-json-schema/reference"
  reading[1]: validate-reference-data-with-json-schema
  provenance: "Original editorial reference notes by YJTOON, informed by the linked primary documentation. External specifications retain their own licenses."
  entry_count: 16
  fields[4]{section,field,type,example}:
    data,keyword,string,type
    data,example,string,"{\"type\":\"string\"}"
    data,purpose,string,Constrain the JSON value type.
    data,pitfall,string,A numeric-looking string is still a string.
data[16]{keyword,example,purpose,pitfall}:
  type,"{\"type\":\"string\"}",Constrain the JSON value type.,A numeric-looking string is still a string.
  properties,"{\"properties\":{\"name\":{\"type\":\"string\"}}}",Validate named object properties.,Listed properties are optional unless required says otherwise.
  required,"{\"required\":[\"name\"]}",Require object property presence.,Presence does not exclude an empty string or null by itself.
  additionalProperties,"{\"additionalProperties\":false}",Restrict properties not covered by properties or patternProperties.,Composition can require unevaluatedProperties instead.
  unevaluatedProperties,"{\"unevaluatedProperties\":false}",Restrict properties left unevaluated across applicable subschemas.,Use a validator with the correct draft support.
  items,"{\"items\":{\"type\":\"integer\"}}",Validate array items with one schema.,It does not require a nonempty array.
  prefixItems,"{\"prefixItems\":[{\"type\":\"string\"},{\"type\":\"integer\"}]}",Validate positional array elements.,Length constraints are separate.
  minItems,"{\"minItems\":1}",Require a minimum array length.,It does not constrain each item’s type.
  enum,"{\"enum\":[\"json\",\"yaml\",\"toon\"]}",Accept one of an explicit set of values.,Values are case sensitive.
  const,"{\"const\":\"ready\"}",Accept one exact JSON value.,It can constrain more than strings.
  minimum,"{\"minimum\":0}",Set an inclusive numeric lower bound.,Strings are not numeric values.
  pattern,"{\"pattern\":\"^[A-Z]{2}$\"}",Validate a string with a regular expression.,Patterns are not anchored automatically.
  allOf,"{\"allOf\":[{\"type\":\"integer\"},{\"minimum\":0}]}",Require every subschema to pass.,"It is logical intersection, not object inheritance."
  anyOf,"{\"anyOf\":[{\"type\":\"string\"},{\"type\":\"number\"}]}",Require at least one passing subschema.,Multiple matches are allowed.
  oneOf,"{\"oneOf\":[{\"const\":\"a\"},{\"const\":\"b\"}]}",Require exactly one passing subschema.,Overlapping alternatives cause rejection.
  format,"{\"format\":\"date-time\"}",Annotate a string with a named semantic format.,Assertion behavior depends on the dialect and validator.