Getting Started

Compiling and Installing Jansson

The Jansson source is available at

Unix-like systems (including MinGW)

Unpack the source tarball and change to the source directory:

bunzip2 -c jansson-2.14.tar.bz2 | tar xf -
cd jansson-2.14

The source uses GNU Autotools (autoconf, automake, libtool), so compiling and installing is extremely simple:

make check
make install

To change the destination directory (/usr/local by default), use the --prefix=DIR argument to ./configure. See ./configure --help for the list of all possible configuration options.

The command make check runs the test suite distributed with Jansson. This step is not strictly necessary, but it may find possible problems that Jansson has on your platform. If any problems are found, please report them.

If you obtained the source from a Git repository (or any other source control system), there’s no ./configure script as it’s not kept in version control. To create the script, the build system needs to be bootstrapped. There are many ways to do this, but the easiest one is to use autoreconf:

autoreconf -fi

This command creates the ./configure script, which can then be used as described above.

CMake (various platforms, including Windows)

Jansson can be built using CMake. Create a build directory for an out-of-tree build, change to that directory, and run cmake (or ccmake, cmake-gui, or similar) to configure the project.

See the examples below for more detailed information.


In the below examples .. is used as an argument for cmake. This is simply the path to the jansson project root directory. In the example it is assumed you’ve created a sub-directory build and are using that. You could use any path you want.

Unix (Make files)

Generating make files on unix:

bunzip2 -c jansson-2.14.tar.bz2 | tar xf -
cd jansson-2.14

mkdir build
cd build
cmake .. # or ccmake .. for a GUI.


If you don’t want to build docs or Sphinx is not installed, you should add "-DJANSSON_BUILD_DOCS=OFF" in the cmake command.

Then to build:

make check
make install

Windows (Visual Studio)

Creating Visual Studio project files from the command line:

cd jansson-2.14

md build
cd build
cmake -G "Visual Studio 15 2017" ..


You should replace the name of the generator (-G flag) matching the Visual Studio version installed on your system. Currently, the following versions are supported:

  • Visual Studio 9 2008
  • Visual Studio 10 2010
  • Visual Studio 11 2012
  • Visual Studio 12 2013
  • Visual Studio 14 2015
  • Visual Studio 15 2017
  • Visual Studio 16 2019

Any later version should also work.

You will now have a Visual Studio Solution in your build directory. To run the unit tests build the RUN_TESTS project.

If you prefer a GUI the cmake line in the above example can be replaced with:

cmake-gui ..

For command line help (including a list of available generators) for CMake simply run:


To list available CMake settings (and what they are currently set to) for the project, run:

cmake -LH ..

Windows (MinGW)

If you prefer using MinGW on Windows, make sure MinGW installed and {MinGW}/bin has been added to PATH, then do the following commands:

cd jansson-2.14

md build
cd build
cmake -G "MinGW Makefiles" ..

Mac OSX (Xcode)

If you prefer using Xcode instead of make files on OSX, do the following. (Use the same steps as for Unix):

cmake -G "Xcode" ..

Additional CMake settings

Shared library

By default the CMake project will generate build files for building the static library. To build the shared version use:

Changing install directory (same as autoconf –prefix)

Just as with the autoconf project you can change the destination directory for make install. The equivalent for autoconfs ./configure --prefix in CMake is:

cmake -DCMAKE_INSTALL_PREFIX:PATH=/some/other/path ..
make install


Jansson can be built for Android platforms. is in the source root directory. The configuration header file is located in the android directory in the source distribution.

Other Systems

On non Unix-like systems, you may be unable to run the ./configure script. In this case, follow these steps. All the files mentioned can be found in the src/ directory.

  1. Create jansson_config.h (which has some platform-specific parameters that are normally filled in by the ./configure script). Edit, replacing all @variable@ placeholders, and rename the file to jansson_config.h.
  2. Make jansson.h and jansson_config.h available to the compiler, so that they can be found when compiling programs that use Jansson.
  3. Compile all the .c files (in the src/ directory) into a library file. Make the library available to the compiler, as in step 2.

Building the Documentation

(This subsection describes how to build the HTML documentation you are currently reading, so it can be safely skipped.)

Documentation is in the doc/ subdirectory. It’s written in reStructuredText with Sphinx annotations. To generate the HTML documentation, invoke:

make html

and point your browser to doc/_build/html/index.html. Sphinx 1.0 or newer is required to generate the documentation.

Compiling Programs that Use Jansson

Jansson involves one C header file, jansson.h, so it’s enough to put the line

#include <jansson.h>

in the beginning of every source file that uses Jansson.

There’s also just one library to link with, libjansson. Compile and link the program as follows:

cc -o prog prog.c -ljansson

Starting from version 1.2, there’s also support for pkg-config:

cc -o prog prog.c `pkg-config --cflags --libs jansson`