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Command-line tools for converting between MessagePack and JSON /[UNIX Shell]


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msgpack-tools contains simple command-line utilities for converting from MessagePack to JSON and vice-versa. They support options for lax parsing, lossy conversions, pretty-printing, and base64 encoding.

  • msgpack2json -- Convert MessagePack to JSON
  • json2msgpack -- Convert JSON to MessagePack

They can be used for dumping MessagePack from a file or web API to a human-readable format, or for converting hand-written or generated JSON to MessagePack. The lax parsing mode supports comments and trailing commas in JSON, making it possible to hand-write your app or game data in JSON and convert it at build-time to MessagePack.

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To view a MessagePack file in a human-readable format for debugging purposes:

msgpack2json -di

To convert a hand-written JSON file to a MessagePack file, ignoring comments and trailing commas, and allowing embedded base64 with a base64: prefix:

json2msgpack -bli file.json -o

To fetch MessagePack from a web API and view it in a human-readable format:

curl 'http://example/api/url' | msgpack2json -d

To view the MessagePack-equivalent encoding of a JSON string:

$ echo '{"compact": true, "schema": 0}' | json2msgpack | hexdump -C
00000000  82 a7 63 6f 6d 70 61 63  74 c3 a6 73 63 68 65 6d  |..compact..schem|
00000010  61 00                                             |a.|

To test a MessagePack-RPC server via netcat:

$ echo '[0,0,"sum",[1,2]]' | json2msgpack | nc -q1 localhost 18800 | msgpack2json -d


  • Arch Linux: msgpack-tools in the AUR, e.g. yaourt -S msgpack-tools

  • Mac OS X (Homebrew): brew install

  • Debian (Ubuntu, etc.): .deb package for x86_64 in the latest release; install with dpkg

For other platforms, msgpack-tools must be built from source. Download the msgpack-tools tarball from the latest release page (not the "source code" archive generated by GitHub, but the actual release package.)

msgpack-tools uses CMake. A configure wrapper is provided that calls CMake, so you can simply run the usual:

./configure && make && sudo make install

If you are building from the repository, you will need md2man to generate the man pages.

Differences between MessagePack and JSON

MessagePack is intended to be very close to JSON in supported features, so they can usually be transparently converted from one to the other. There are some differences, however, which can complicate conversions.

These are the differences in what objects are representable in each format:

  • JSON keys must be strings. MessagePack keys can be any type, including maps and arrays.

  • JSON supports "bignums", i.e. integers of any size. MessagePack integers must fit within a 64-bit signed or unsigned integer.

  • JSON real numbers are specified in decimal scientific notation and can have arbitrary precision. MessagePack real numbers are in IEEE 754 standard 32-bit or 64-bit binary.

  • MessagePack supports binary and extension type objects. JSON does not support binary data. Binary data is often encoded into a base64 string to be embedded into a JSON document.

  • A JSON document can be encoded in UTF-8, UTF-16 or UTF-32, and the entire document must be in the same encoding. MessagePack strings are required to be UTF-8, although this is not enforced by many encoding/decoding libraries.

By default, msgpack2json and json2msgpack convert in strict mode. If an object in the source format is not representable in the destination format, the converter aborts with an error. A lax mode is available which performs a "lossy" conversion, and base64 conversion modes are available to support binary data in JSON.