JSON Schema validator. Supports drafts 4, 6, and 7.


Add this line to your application's Gemfile:

gem 'json_schemer'

And then execute:

$ bundle

Or install it yourself as:

$ gem install json_schemer


require 'json_schemer'

schema = {
  'type' => 'object',
  'properties' => {
    'abc' => {
      'type' => 'integer',
      'minimum' => 11
schemer = JSONSchemer.schema(schema)

# true/false validation

schemer.valid?({ 'abc' => 11 })
# => true

schemer.valid?({ 'abc' => 10 })
# => false

# error validation (`validate` returns an enumerator)

schemer.validate({ 'abc' => 10 }).to_a
# => [{"data"=>10, "schema"=>{"type"=>"integer", "minimum"=>11}, "pointer"=>"#/abc", "type"=>"minimum"}]

# default property values

data = {}
    'properties' => {
      'foo' => {
        'default' => 'bar'
  insert_property_defaults: true
# => {"foo"=>"bar"}

# schema files

require 'pathname'

schema = Pathname.new('/path/to/schema.json')
schemer = JSONSchemer.schema(schema)

# schema json string

schema = '{ "type": "integer" }'
schemer = JSONSchemer.schema(schema)



  # validate `format` (https://tools.ietf.org/html/draft-handrews-json-schema-validation-00#section-7)
  # true/false
  # default: true
  format: true,

  # insert default property values during validation
  # true/false
  # default: false
  insert_property_defaults: true,

  # modify properties during validation. You can pass one Proc or a list of Procs to modify data.
  # Proc/[Proc]
  # default: nil
  before_property_validation: proc do |data, property, property_schema, _parent|
    data[property] ||= 42

  # modify properties after validation. You can pass one Proc or a list of Procs to modify data.
  # Proc/[Proc]
  # default: nil
  after_property_validation: proc do |data, property, property_schema, _parent|
    data[property] = Date.iso8601(data[property]) if property_schema.is_a?(Hash) && property_schema['format'] == 'date'

  # resolve external references
  # 'net/http'/proc/lambda/respond_to?(:call)
  # 'net/http': proc { |uri| JSON.parse(Net::HTTP.get(uri)) }
  # default: proc { |uri| raise UnknownRef, uri.to_s }
  ref_resolver: 'net/http'


The json_schemer executable takes a JSON schema file as the first argument followed by one or more JSON data files to validate. If there are any validation errors, it outputs them and returns an error code.

Validation errors are output as single-line JSON objects. The --errors option can be used to limit the number of errors returned or prevent output entirely (and fail fast).

The schema or data can also be read from stdin using -.

% json_schemer --help
  json_schemer [options] <schema> <data>...
  json_schemer [options] <schema> -
  json_schemer [options] - <data>...
  json_schemer -h | --help
  json_schemer --version

  -e, --errors MAX                 Maximum number of errors to output
                                   Use "0" to validate with no output
  -h, --help                       Show help
  -v, --version                    Show version


After checking out the repo, run bin/setup to install dependencies. Then, run rake test to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

Build Status

Build Status


Bug reports and pull requests are welcome on GitHub at https://github.com/davishmcclurg/json_schemer.


The gem is available as open source under the terms of the MIT License.