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A JSON Parser-Generator that takes a json-schema and converts it into a parser.

It supports a subset of json-schema, and changes some of the default assumptions of the spec to be stricter--eg it effectively sets the additionalProperties field to false by not allowing unspecified fields. It also doesn't allow patternProperties, or enum. It definitely doesn't follow the Hyper-Schema stuff. If you want to use a portion of someone elses' schema, you'll need to drop it into yours directly.


Using a parser to handle inputs makes your app safe from attacks that rely on passing disallowed params, because disallowed params will either be ignored or rejected.

Be definite about what you accept.(*)

Treat inputs as a language, accept it with a matching computational power, generate its recognizer from its grammar.

Treat input-handling computational power as privilege, and reduce it whenever possible.


Add this line to your application's Gemfile:

gem 'muskox'

And then execute:

$ bundle

Or install it yourself as:

$ gem install muskox


    # to generate a parser, call generate w/ a JSON-Schema
    parser = Muskox.generate({
        "title" => "Schema",
        "type" => "object",
        "properties" => {
          "number" => {
            "type" => "integer"
        "required" => ["number"]

    # then call parse with the string you want to have parsed
    n = parser.parse "{\"number\": 1}"
    # => {"number" => 1}
    # invalid types are disallowed
    parser.parse "{\"number\": true}" rescue puts $!


  • performance improvements/testing
    • Ruby is slow & the lexer uses Regex. We should do something better
    • for JRuby: Jackson has a streaming interface that looks interesting
  • fuzz testing
    • needs more tests that try to break it
  • better JSON-schema support
    • maybe instead of reassuming the default for additionalProperties, we should validate schemas and say "Muskox requires additionalProperties: false"
  • more information on errors
  • add option to ignore additional properties (not particularly safe...)


  1. Fork it
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create new Pull Request


A JSON Schema based parser generator




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