MessagePack is an efficient binary serialization format. It lets you exchange data among multiple languages like JSON but it's faster and smaller. For example, small integers (like flags or error code) are encoded into a single byte, and typical short strings only require an extra byte in addition to the strings themselves.

If you ever wished to use JSON for convenience (storing an image with metadata) but could not for technical reasons (binary data, size, speed...), MessagePack is a perfect replacement.

require 'msgpack'
msg = [1,2,3].to_msgpack  #=> "\x93\x01\x02\x03"
MessagePack.unpack(msg)   #=> [1,2,3]

Use RubyGems to install:

gem install msgpack

or build msgpack-ruby and install:

gem install --local pkg/msgpack

Use cases


MessagePack for Ruby should run on x86, ARM, PowerPC, SPARC and other CPU architectures.

And it works with MRI (CRuby) and Rubinius. Patches to improve portability is highly welcomed.

Serializing objects

Use MessagePack.pack or to_msgpack:

require 'msgpack'
msg = MessagePack.pack(obj)  # or
msg = obj.to_msgpack

Streaming serialization

Packer provides advanced API to serialize objects in streaming style:

# serialize a 2-element array [e1, e2]
pk =

See API reference for details.

Deserializing objects

Use MessagePack.unpack:

require 'msgpack'
obj = MessagePack.unpack(msg)

Streaming deserialization

Unpacker provides advanced API to deserialize objects in streaming style:

# deserialize objects from an IO
u =
u.each do |obj|
  # ...

or event-driven style which works well with EventMachine:

# event-driven deserialization
def on_read(data)
  @u ||=
  @u.feed_each(data) {|obj|
     # ...

See API reference for details.

Buffer API

MessagePack for Ruby provides a buffer API so that you can read or write data by hand, not via Packer or Unpacker API.

This MessagePack::Buffer is backed with a fixed-length shared memory pool which is very fast for small data (<= 4KB), and has zero-copy capability which significantly affects performance to handle large binary data.

How to build and run tests

Before building msgpack, you need to install bundler and dependencies.

gem install bundler
bundle install

Then, you can run the tasks as follows:



Sadayuki Furuhashi <>


Copyright (c) 2008-2013 Sadayuki Furuhashi


Apache License, Version 2.0