package jsonschema-core

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ocaml-jsonschema

JSON Schema draft-07 validator for OCaml.

Pure OCaml implementation. Compiles schemas into validator functions for repeated use.

Packages

  • jsonschema-core — $ref resolution, JSON Pointer, registry, regex engine, instance model
  • jsonschema-validation — All 37 draft-07 validation keywords + 17 format validators

Installation

opam pin add jsonschema-core .
opam pin add jsonschema-validation .

Usage

let schema = Yojson.Safe.from_string {|{
  "type": "object",
  "properties": {
    "name": { "type": "string" },
    "age": { "type": "integer", "minimum": 0 }
  },
  "required": ["name"]
}|}

let validate = Jsonschema_validation.compile schema

let () =
  let data = Yojson.Safe.from_string {|{"name": "Alice", "age": 30}|} in
  match validate data with
  | [] -> print_endline "valid"
  | errors -> List.iter (fun e -> print_endline (Jsonschema_core.Error.to_string e)) errors

Validation keywords

  • Type: type, enum, const
  • Numeric: multipleOf, maximum, exclusiveMaximum, minimum, exclusiveMinimum
  • String: maxLength, minLength, pattern
  • Array: items, additionalItems, maxItems, minItems, uniqueItems, contains
  • Object: properties, patternProperties, additionalProperties, maxProperties, minProperties, required, dependencies, dependentRequired, propertyNames
  • Logic: allOf, anyOf, oneOf, not
  • Conditional: if/then/else
  • Format: date-time, date, time, email, idn-email, hostname, idn-hostname, uri, uri-reference, iri, iri-reference, uri-template, ipv4, ipv6, json-pointer, relative-json-pointer, regex
  • Content: contentEncoding (base64), contentMediaType (application/json)

Format validation

Format validators cover RFC 3339 (date/time with leap second UTC conversion), RFC 3986/3987 (URI/IRI with percent-encoding and port validation), RFC 5890/5891/5892/5893 (IDNA2008 hostnames via ocaml-idna), and RFC 5321 (email).

Test suite results

JSON-Schema-Test-Suite draft-07:

  • Mandatory: 922/922 (100%)
  • Format: 535/535 (100%)
  • Optional: 98/118 (83.1%)
  • Total: 1555/1575 (98.7%)

Known limitations

20 optional test failures related to ECMA-262 regex Unicode semantics. The re library (ocaml/ocaml-re) operates at byte level without Unicode codepoint support. Affected patterns: \D, \W, \S on multi-byte characters, \uXXXX escapes, UTF-16 surrogate pairs, and Unicode character classes in pattern/patternProperties. Tracking: ocaml-re#24, ocaml-re#592.

License

ISC