JSON Schema documents compiled and validated by Formata.Backplane.JsonSchema.

Documents are JSON-compatible maps (string keys) or the boolean schemas true/false. They are handed to Formata.Backplane.JsonSchema as they are; Formata never converts them to native schemas.

Dialects

Draft 2020-12 and Draft 7 are supported.

• A recognized root $schema selects the dialect: https://json-schema.org/draft/2020-12/schema or http://json-schema.org/draft-07/schema#.

• dialect: :draft7 | :draft2020_12 selects it explicitly. Conflicting with the document's $schema is a :schema / :dialect_conflict error.

• Without either, Draft 2020-12 is used.
• A $schema that is not one of the recognized meta-schemas is rejected (:schema / :unknown_dialect) unless dialect: is given or a :loader is provided to resolve the custom meta-schema and its vocabularies.

Unknown keywords and extension keywords (for example x-*) are accepted as annotations, as the dialects permit.

Format assertion

format is an annotation by default and does not reject data. Pass format_assertion: true to assert the formats implemented by Formata.Backplane.JsonSchema (email, date-time, date, time, uri, ipv4, ipv6, hostname, regex, uuid, ...). Unknown format names are always accepted. In Draft 2020-12, a custom meta-schema that enables the format-assertion vocabulary also enables assertion; a document without $schema uses the standard vocabularies, in which format is an annotation.

Internationalized names cannot be checked without the IDNA2008 Unicode tables, which Formata does not include. When hostname, email, idn-hostname, or idn-email is asserted and the value contains an A-label (xn--...) or a non-ASCII label, validation stops with a single :unsupported / :unsupported_format error at the value's path: the value is neither accepted nor rejected as if it had been checked, and the result cannot be inverted by not, anyOf, oneOf, or if. A value that is invalid for another reason (for example an ASCII label with _) is still a :validation / :format error. Plain ASCII host names are fully checked.

References

Local references (#/$defs/..., #anchor, embedded $id resources) are resolved without any I/O. Remote references are only loaded through an explicit :loader function (uri -> {:ok, map | boolean} | {:error, term}); Formata performs no network access. A reference that cannot be resolved fails validation with a :schema / :unresolved_ref error, never a silent pass.

Defaults and other annotations

default, examples, title, and other annotations never modify data. Formata.cast/3 is not available for JSON Schemas because they define no transformations.

Data model

Data must be in the JSON data model: nil, booleans, numbers, strings, lists, and maps with string keys. Other terms (atom keys, Date, tuples, special-float atoms, ...) are reported as :unsupported / :non_json_value; convert them explicitly first (see Formata.Transform).

Additional properties are governed only by the document (additionalProperties, unevaluatedProperties); there is no facade option that overrides them.