msgpack2json and json2msgpack are 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.

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.

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

msgpack2json -di file.mp

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 file.mp

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

curl http://example/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.|
00000012

msgpack2json currently must be built from source. The latest version of the msgpack2json source archive can be downloaded from the releases page. This includes the library dependencies and has pre-generated man pages:

https://github.com/ludocode/msgpack2json/releases

msgpack2json uses CMake. A configure script is provided that calls CMake, so on Linux and Mac OS X, you can simply run the usual:

./configure && make && sudo make install

If you are building from the repository, you will need to fetch the dependencies and generate the man pages. These are done with the scripts under tools/fetch.sh and tools/man.sh. md2man is required to generate the man pages.

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.

• 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.

• The top-level object in a JSON document must be either an array or object (map). The top-level object in MessagePack can be any type.

• A JSON document must be entirely in one encoding. MessagePack does not specify encoding, and different strings in the same document can technically be in different encodings (though this is a really bad idea.)

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.