JSON-Fortran: A Modern Fortran JSON API

Table of Contents


Build Status GitHub issues Codecov last-commit

Take a look at the CHANGELOG for a list of changes since the latest release.


Brief description

JSON-Fortran is a user-friendly, thread-safe, and object-oriented API for reading and writing JSON files, written in modern Fortran.



GitHub release homebrew version Conda (channel only)

Download the official versioned releases here. Or, get the latest development code from the master branch here.

NEWS: As of June 7, 2015, json-fortran can be downloaded and installed with the homebrew package manager on Mac OS X. Once homebrew is installed, make sure that the formulae are up to date, view the package options and caveats, and install the json-fortran formula:

brew update
brew info json-fortran
brew install --with-unicode-support json-fortran

Please note, if you wish to support usage of JSON-Fortran with multiple Fortran compilers, please follow the CMake installation instructions below, as the homebrew installation is only intended to support a single Fortran compiler. Cheers!

NEWS: As of January 20, 2022, json-fortran can be downloaded and installed via the conda package manager on Mac OS X and Linux. Once a conda-distribution, like miniforge, is installed the json-fortran package can be installed.

conda install json-fortran

Note: Packages on conda-forge are build with GCC 9.4 which is upwards compatible with newer GCC versions, but not with other Fortran compilers.


Building the library

The code requires a Fortran compiler that supports various Fortran 2003 and Fortran 2008 features such as: allocatable strings, newunit, generic, class, and abstract interface. It has been successfully compiled with the Intel Fortran compiler 13.1.0 (and greater) and the GNU gfortran compiler [4.9 and greater]. It has also been reported that the library can be built (using the CMake build script) with the NAG Fortran compiler 6.0

Currently, several ways are provided to build the JSON-fortran library (libjsonfortran).

  • A build script, is provided in the project root directory. This script uses FoBiS to build the JSON-Fortran library and the unit tests on Unix-like systems. Edit the script to use either the Intel Fortran Compiler or Gfortran. Note that version 1.2.5 of FoBiS (or later) is required.

  • A FoBiS configuration file (json-fortran.fobis) is also provided that can also build the library and examples. Use the mode flag to indicate what to build. For example:

  • To build all the examples using gfortran: build -f json-fortran.fobis -mode tests-gnu

  • To build all the examples using ifort: build -f json-fortran.fobis -mode tests-intel
  • To build a static library using gfortran: build -f json-fortran.fobis -mode static-gnu
  • To build a static library using ifort: build -f json-fortran.fobis -mode static-intel

The full set of modes are: static-gnu, static-gnu-debug, static-intel, static-intel-debug, shared-gnu, shared-gnu-debug, shared-intel, shared-intel-debug, tests-gnu, tests-gnu-debug, tests-intel, tests-intel-debug

To generate the documentation using ford, run: rule --execute makedoc -f json-fortran.fobis

To run all the tests, run: rule --execute tests -f json-fortran.fobis

  • A Visual Studio project is included for building the library (and unit tests) on Windows with the Intel Fortran Compiler. The project has been tested with Visual Studio 2010 and 2013.

  • A CMake build system is provided. This build system has been tested on Mac and Linux using the Intel Fortran Compiler, gfortran 4.9, and NAG Fortran 6.0. It does also work on Windows (but note that the Visual Studio project it generates is not quite the same as the one mentioned above). This CMake based build provides an install target, and exports from both the install location and the build location so that building and using JSON-Fortran in another CMake based project is trivial. To get started with the CMake based build, set the environment variable FC to point to your Fortran compiler, and create a build directory. Then (cmake-gui|ccmake|cmake) /path/to/json-fortran-root to configure, make to build and make install to optionally install. You can also use make check to build and run the unit tests. As long as the project is built with CMake, other CMake projects can find it and link against it. For example, if you have a second copy of the JSON-Fortran project tree, and want to build the unit tests linking against those compiled/installed by the first copy:

cmake_minimum_required ( VERSION 2.8.8 FATAL_ERROR )
enable_language ( Fortran )
project ( jf_test NONE )

find_package ( jsonfortran-${CMAKE_Fortran_COMPILER_ID} 8.3.0 REQUIRED )

file ( GLOB JF_TEST_SRCS "src/tests/jf_test_*.F90" )
foreach ( UNIT_TEST ${JF_TEST_SRCS} )
  get_filename_component ( TEST ${UNIT_TEST} NAME_WE )
  add_executable ( ${TEST} ${UNIT_TEST} )
  target_link_libraries ( ${TEST} jsonfortran::jsonfortran-static )
  # or for linking against the dynamic/shared library:
  # target_link_libraries ( ${TEST} jsonfortran::jsonfortran ) # instead



The API documentation for the latest release version can be found here. The documentation can also be generated by processing the source files with FORD. Note that both the shell script and CMake will also generate these files automatically in the documentation folder, assuming you have FORD installed.

Some examples can also be found on the wiki.



Want to help? Take a quick look at our contributing guidelines then claim something and Fork. Commit. Pull request.



The JSON-Fortran source code and related files and documentation are distributed under a permissive free software license (BSD-style). See the LICENSE file for more details.



  • JSON-Fortran is a fork and extensive upgrade of the Fortran 95 FSON code. The reason for the split was to be able to incorporate object-oriented and other nice features of the Fortran 2003 and 2008 standards. Many thanks to the original authors of FSON.
  • For more information about JSON, see:
  • json-fortran on Codecov.IO