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Lots of Ruby libraries parse JSON and everyone has their favorite JSON coder. Instead of choosing a single JSON coder and forcing users of your library to be stuck with it, you can use MultiJSON instead, which will simply choose the fastest available JSON coder. Here's how to use it:

require 'multi_json'

MultiJson.load('{"abc":"def"}') #=> {"abc" => "def"}
MultiJson.load('{"abc":"def"}', :symbolize_keys => true) #=> {:abc => "def"}
MultiJson.dump({:abc => 'def'}) # convert Ruby back to JSON
MultiJson.dump({:abc => 'def'}, :pretty => true) # encoded in a pretty form (if supported by the coder)

When loading invalid JSON, MultiJSON will throw a MultiJson::ParseError. MultiJson::DecodeError and MultiJson::LoadError are aliases for backwards compatibility.

  MultiJson.load('{invalid json}')
rescue MultiJson::ParseError => exception # => "{invalid json}"
  exception.cause # => JSON::ParserError: 795: unexpected token at '{invalid json}'

ParseError instance has cause reader which contains the original exception. It also has data reader with the input that caused the problem.

The use method, which sets the MultiJSON adapter, takes either a symbol or a class (to allow for custom JSON parsers) that responds to both .load and .dump at the class level.

When MultiJSON fails to load the specified adapter, it'll throw MultiJson::AdapterError which inherits from ArgumentError.

MultiJSON tries to have intelligent defaulting. That is, if you have any of the supported engines already loaded, it will utilize them before attempting to load any. When loading, libraries are ordered by speed. First Oj, then Yajl, then the JSON gem, then JSON pure. If no other JSON library is available, MultiJSON falls back to OkJson, a simple, vendorable JSON parser.

Supported JSON Engines

  • Oj Optimized JSON by Peter Ohler
  • Yajl Yet Another JSON Library by Brian Lopez
  • JSON The default JSON gem with C-extensions (ships with Ruby 1.9+)
  • JSON Pure A Ruby variant of the JSON gem
  • gson.rb A Ruby wrapper for google-gson library (JRuby only)
  • JrJackson JRuby wrapper for Jackson (JRuby only)
  • OkJson A simple, vendorable JSON parser

Supported Ruby Versions

This library aims to support and is [tested against][action] the following Ruby implementations:

  • Ruby 3.0
  • Ruby 3.1
  • Ruby 3.2
  • Ruby 3.3
  • JRuby 9.4

If something doesn't work in one of these implementations, it's a bug.

This library may inadvertently work (or seem to work) on other Ruby implementations, however support will only be provided for the versions listed above.

If you would like this library to support another Ruby version, you may volunteer to be a maintainer. Being a maintainer entails making sure all tests run and pass on that implementation. When something breaks on your implementation, you will be responsible for providing patches in a timely fashion. If critical issues for a particular implementation exist at the time of a major release, support for that Ruby version may be dropped.


This library aims to adhere to Semantic Versioning 2.0.0. Violations of this scheme should be reported as bugs. Specifically, if a minor or patch version is released that breaks backward compatibility, that version should be immediately yanked and/or a new version should be immediately released that restores compatibility. Breaking changes to the public API will only be introduced with new major versions. As a result of this policy, you can (and should) specify a dependency on this gem using the Pessimistic Version Constraint with two digits of precision. For example:

spec.add_dependency 'multi_json', '~> 1.0'


Copyright (c) 2010-2024 Michael Bleigh, Josh Kalderimis, Erik Berlin, and Pavel Pravosud. See LICENSE for details.