From 967a5db20a8beb6585471dcd06d8f755cb58c87c Mon Sep 17 00:00:00 2001
From: Sebastian Ehlert <28669218+awvwgk@users.noreply.github.com>
Date: Sat, 15 Jan 2022 17:03:42 +0100
Subject: [PATCH] Add support for reading QCSchema JSON

- allow automatic detection of jsonfortran installations via CMake
- subproject fallback support for meson
---
 .github/workflows/build.yml                   |   2 +-
 CMakeLists.txt                                |  18 +
 README.md                                     |   4 +-
 config/CMakeLists.txt                         |  20 +
 config/cmake/Findjsonfortran.cmake            |  30 ++
 config/meson.build                            |  11 +
 config/template.cmake                         |   5 +
 config/template.pc                            |   1 +
 doc/format-qcschema.md                        |  94 ++++
 doc/index.md                                  |   1 +
 fpm.toml                                      |   3 +
 include/mctc/defs.h                           |   8 +
 man/mctc-convert.1.adoc                       |   1 +
 meson.build                                   |   6 +-
 meson_options.txt                             |   8 +
 src/mctc/CMakeLists.txt                       |   2 +-
 src/mctc/io/read.f90                          |   4 +
 src/mctc/io/read/CMakeLists.txt               |   1 +
 src/mctc/io/read/meson.build                  |   1 +
 src/mctc/io/read/qcschema.F90                 | 180 +++++++
 src/mctc/meson.build                          |   2 +-
 src/mctc/{version.f90 => version.F90}         |  26 +-
 subprojects/.gitignore                        |   2 +
 subprojects/json-fortran-8.2.5.wrap           |   8 +
 .../json-fortran-8.2.5/meson.build            |  28 +
 test/CMakeLists.txt                           |   1 +
 test/main.f90                                 |   2 +
 test/meson.build                              |   1 +
 test/test_read.f90                            |  92 ++++
 test/test_read_qcschema.f90                   | 477 ++++++++++++++++++
 test/test_write.f90                           |  26 +
 31 files changed, 1058 insertions(+), 7 deletions(-)
 create mode 100644 config/cmake/Findjsonfortran.cmake
 create mode 100644 doc/format-qcschema.md
 create mode 100644 include/mctc/defs.h
 create mode 100644 src/mctc/io/read/qcschema.F90
 rename src/mctc/{version.f90 => version.F90} (77%)
 create mode 100644 subprojects/.gitignore
 create mode 100644 subprojects/json-fortran-8.2.5.wrap
 create mode 100644 subprojects/packagefiles/json-fortran-8.2.5/meson.build
 create mode 100644 test/test_read_qcschema.f90

diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 16d48ff2..5b04c74a 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -144,7 +144,7 @@ jobs:
       if: ${{ matrix.build == 'fpm' }}
       uses: fortran-lang/setup-fpm@v3
       with:
-        fpm-version: 'v0.2.0'
+        fpm-version: 'v0.3.0'
 
     - name: Prepare for cache restore
       if: ${{ matrix.compiler == 'intel' }}
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 327427c1..b761907f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -27,6 +27,11 @@ include(GNUInstallDirs)
 # General configuration information
 add_subdirectory("config")
 
+# Dependencies
+if(NOT TARGET "jsonfortran::jsonfortran" AND WITH_JSON)
+  find_package("jsonfortran" REQUIRED)
+endif()
+
 # Collect source of the project
 set(srcs)
 add_subdirectory("src")
@@ -36,6 +41,18 @@ add_library(
   "${PROJECT_NAME}-lib"
   "${srcs}"
 )
+target_compile_definitions(
+  "${PROJECT_NAME}-lib"
+  PRIVATE
+  "WITH_JSON=$<BOOL:${WITH_JSON}>"
+)
+if(WITH_JSON)
+  target_link_libraries(
+    "${PROJECT_NAME}-lib"
+    PRIVATE
+    "jsonfortran::jsonfortran"
+  )
+endif()
 set_target_properties(
   "${PROJECT_NAME}-lib"
   PROPERTIES
@@ -48,6 +65,7 @@ set_target_properties(
 target_include_directories(
   "${PROJECT_NAME}-lib"
   PUBLIC
+  $<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/include>
   $<BUILD_INTERFACE:${PROJECT_BINARY_DIR}/include>
   $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>
   $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}/${module-dir}>
diff --git a/README.md b/README.md
index 6ad55873..8bcd655d 100644
--- a/README.md
+++ b/README.md
@@ -11,11 +11,11 @@
 
 To build this project from the source code in this repository you need to have
 a Fortran compiler supporting Fortran 2008 and one of the supported build systems:
-- [meson](https://mesonbuild.com) version 0.53 or newer, with
+- [meson](https://mesonbuild.com) version 0.55 or newer, with
   a build-system backend, *i.e.* [ninja](https://ninja-build.org) version 1.7 or newer
 - [cmake](https://cmake.org) version 3.14 or newer, with
   a build-system backend, *i.e.* [ninja](https://ninja-build.org) version 1.10 or newer
-- [fpm](https://github.com/fortran-lang/fpm) version 0.2.0 or newer
+- [fpm](https://github.com/fortran-lang/fpm) version 0.3.0 or newer
 
 Currently this project supports GCC, Intel and PGI/NVHPC compilers.
 
diff --git a/config/CMakeLists.txt b/config/CMakeLists.txt
index 7e797f4f..80d33e63 100644
--- a/config/CMakeLists.txt
+++ b/config/CMakeLists.txt
@@ -15,6 +15,7 @@
 option(BUILD_SHARED_LIBS "Whether the libraries built should be shared" FALSE)
 
 option(WITH_OpenMP "Enable support for shared memory parallelisation with OpenMP" TRUE)
+option(WITH_JSON "Enable support for JSON parsing via json-fortran" FALSE)
 
 set(
   module-dir
@@ -22,6 +23,14 @@ set(
 )
 set(module-dir "${module-dir}" PARENT_SCOPE)
 
+list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/cmake")
+set(CMAKE_MODULE_PATH "${CMAKE_MODULE_PATH}" PARENT_SCOPE)
+install(
+  DIRECTORY
+  "${CMAKE_CURRENT_SOURCE_DIR}/cmake/"
+  DESTINATION "${CMAKE_INSTALL_LIBDIR}/cmake/${PROJECT_NAME}"
+)
+
 # Set build type as CMake does not provide defaults
 if(NOT CMAKE_BUILD_TYPE AND NOT CMAKE_CONFIGURATION_TYPES)
   set(
@@ -53,6 +62,17 @@ install(
   DESTINATION "${CMAKE_INSTALL_LIBDIR}/cmake/${PROJECT_NAME}"
 )
 
+if(BUILD_SHARED_LIBS)
+  set(PKG_CONFIG_REQUIRES "Requires.private")
+else()
+  set(PKG_CONFIG_REQUIRES "Requires")
+endif()
+if(WITH_JSON)
+  set(PKG_CONFIG_REQUIREMENTS "json-fortran")
+else()
+  set(PKG_CONFIG_REQUIREMENTS)
+endif()
+
 configure_file(
   "${CMAKE_CURRENT_SOURCE_DIR}/template.pc"
   "${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}.pc"
diff --git a/config/cmake/Findjsonfortran.cmake b/config/cmake/Findjsonfortran.cmake
new file mode 100644
index 00000000..81d794c2
--- /dev/null
+++ b/config/cmake/Findjsonfortran.cmake
@@ -0,0 +1,30 @@
+# This file is part of mctc-lib.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+if(NOT TARGET "jsonfortran::jsonfortran")
+  # json-fortran tries to make it hard to get found
+  string(TOLOWER "jsonfortran-${CMAKE_Fortran_COMPILER_ID}" jsonfortran)
+  find_package("${jsonfortran}" CONFIG)
+  add_library("jsonfortran::jsonfortran" IMPORTED INTERFACE)
+  target_link_libraries(
+    "jsonfortran::jsonfortran"
+    INTERFACE
+    "jsonfortran$<$<NOT:$<BOOL:${BUILD_SHARED_LIBS}>>:-static>"
+  )
+  target_include_directories(
+    "jsonfortran::jsonfortran"
+    INTERFACE
+    "${jsonfortran_INCLUDE_DIRS}"
+  )
+endif()
diff --git a/config/meson.build b/config/meson.build
index dfe535e8..5b20cb7b 100644
--- a/config/meson.build
+++ b/config/meson.build
@@ -46,3 +46,14 @@ if get_option('openmp')
   omp_dep = dependency('openmp')
   lib_deps += omp_dep
 endif
+
+jsonfortran_dep = dependency(
+  'json-fortran',
+  required: get_option('json'),
+  fallback: ['json-fortran-8.2.5','jsonfortran_dep'],
+  default_options: [
+    'default_library=static',
+  ],
+  static: get_option('default_library') != 'dynamic',
+)
+lib_deps += jsonfortran_dep
diff --git a/config/template.cmake b/config/template.cmake
index 3a6ae000..0268d954 100644
--- a/config/template.cmake
+++ b/config/template.cmake
@@ -1,6 +1,7 @@
 @PACKAGE_INIT@
 
 set("@PROJECT_NAME@_WITH_OpenMP" @WITH_OpenMP@)
+set("@PROJECT_NAME@_WITH_JSON" @WITH_JSON@)
 
 if(NOT TARGET "@PROJECT_NAME@::@PROJECT_NAME@")
   include("${CMAKE_CURRENT_LIST_DIR}/@PROJECT_NAME@-targets.cmake")
@@ -10,4 +11,8 @@ if(NOT TARGET "@PROJECT_NAME@::@PROJECT_NAME@")
   if(NOT TARGET "OpenMP::OpenMP_Fortran" AND "@PROJECT_NAME@_WITH_OpenMP")
     find_dependency("OpenMP")
   endif()
+
+  if(NOT TARGET "jsonfortran::jsonfortran" AND "@PROJECT_NAME@_WITH_JSON")
+    find_dependency("jsonfortran")
+  endif()
 endif()
diff --git a/config/template.pc b/config/template.pc
index 3d6efbb5..84c3498c 100644
--- a/config/template.pc
+++ b/config/template.pc
@@ -4,6 +4,7 @@ includedir=${prefix}/@CMAKE_INSTALL_INCLUDEDIR@
 
 Name: @PROJECT_NAME@
 Description: @PROJECT_DESCRIPTION@
+@PKG_CONFIG_REQUIRES@: @PKG_CONFIG_REQUIREMENTS@
 Version: @PROJECT_VERSION@
 Libs: -L${libdir} -l@PROJECT_NAME@
 Cflags: -I${includedir} -I${includedir}/@module-dir@
diff --git a/doc/format-qcschema.md b/doc/format-qcschema.md
new file mode 100644
index 00000000..b4db691c
--- /dev/null
+++ b/doc/format-qcschema.md
@@ -0,0 +1,94 @@
+---
+title: QCSchema JSON
+---
+
+## Specification
+
+@Note [Reference](https://molssi-qc-schema.readthedocs.io)
+
+JSON files are identified by the extension ``json`` and parsed following the ``qcschema_molecule`` or ``qcschema_input`` format.
+The ``molecule`` entry from a ``qcschema_input`` will be extracted, but there is no guarantee that the input information will be used by the program.
+
+
+## Example
+
+Caffeine molecule in ``qcschema_molecule`` format.
+
+
+```json
+{
+  "schema_version": 2,
+  "schema_name": "qcschema_molecule",
+  "provenance": {
+    "creator": "mctc-lib",
+    "version": "0.2.3",
+    "routine": "mctc_io_write_qcschema::write_qcschema"
+  },
+  "symbols": [
+    "C", "N", "C", "N", "C", "C", "C", "O", "N", "C", "O", "N",
+    "C", "C", "H", "H", "H", "H", "H", "H", "H", "H", "H", "H"
+  ],
+  "geometry": [
+     2.0280536328008760E+00, 9.2407587256767454E-02,-1.4305223630546618E-01,
+     4.7502035191684326E+00, 2.3810543955731494E-02,-1.4324120887654343E-01,
+     6.3343605825088858E+00, 2.0709504064354083E+00,-1.4229634602115726E-01,
+     8.7286430580574415E+00, 1.3800666865770403E+00,-1.4267429116331171E-01,
+     8.6532430021976250E+00,-1.1931728137816557E+00,-1.4229634602115726E-01,
+     6.2385514889727283E+00,-2.0836115686975827E+00,-1.4210737345008001E-01,
+     5.6327054260991156E+00,-4.6995588701197342E+00,-1.3946175745499875E-01,
+     3.4493163398727531E+00,-5.4809604515240968E+00,-1.4324120887654343E-01,
+     7.7750874644017181E+00,-6.2442206661050452E+00,-1.3114696432760045E-01,
+     1.0302217657417570E+01,-5.3974345751079591E+00,-1.3681614145991747E-01,
+     1.2074024483837716E+01,-6.9158291837135346E+00,-1.3662716888884024E-01,
+     1.0700382864677302E+01,-2.7907469296685923E+00,-1.4154045573684831E-01,
+     1.3246032369658721E+01,-1.7697281281382971E+00,-1.4210737345008001E-01,
+     7.4088586216540389E+00,-8.9590006222005893E+00,-1.1640710378357619E-01,
+     1.3870586717068980E+00, 2.0558326007492296E+00,-1.4172942830792554E-01,
+     1.3462405963542154E+00,-8.6360464982295970E-01, 1.5560001502499454E+00,
+     1.3462405963542154E+00,-8.6133697897003281E-01,-1.8434274308584184E+00,
+     5.6559490523416152E+00, 4.0016831651315083E+00,-1.4135148316577109E-01,
+     1.4674287061860456E+01,-3.2622334945062916E+00,-1.4343018144762065E-01,
+     1.3508893216027154E+01,-6.0811373372653921E-01, 1.5490081651200875E+00,
+     1.3507759380600691E+01,-6.0622400801576681E-01,-1.8320890765937843E+00,
+     5.4140641613627567E+00,-9.4924701903516215E+00,-1.1017100893802745E-01,
+     8.3191394965330758E+00,-9.7494728870166600E+00, 1.5654487788038070E+00,
+     8.3151710725404531E+00,-9.7685591166954602E+00,-1.7910820286700244E+00
+  ],
+  "molecular_charge": 0,
+  "connectivity": [
+    [ 0, 1, 1],
+    [ 1, 2, 4],
+    [ 2, 3, 4],
+    [ 3, 4, 4],
+    [ 1, 5, 1],
+    [ 4, 5, 4],
+    [ 5, 6, 1],
+    [ 6, 7, 2],
+    [ 6, 8, 1],
+    [ 8, 9, 1],
+    [ 9,10, 2],
+    [ 4,11, 1],
+    [ 9,11, 1],
+    [11,12, 1],
+    [ 8,13, 1],
+    [ 0,14, 1],
+    [ 0,15, 1],
+    [ 0,16, 1],
+    [ 2,17, 1],
+    [12,18, 1],
+    [12,19, 1],
+    [12,20, 1],
+    [13,21, 1],
+    [13,22, 1],
+    [13,23, 1]
+  ]
+}
+```
+
+
+## Missing features
+
+The schema is not verified on completeness and not all data is stored in the final structure type.
+
+@Note Feel free to contribute support for missing features
+      or bring missing features to our attention by opening an issue.
diff --git a/doc/index.md b/doc/index.md
index 792733a2..a59df38a 100644
--- a/doc/index.md
+++ b/doc/index.md
@@ -11,3 +11,4 @@ This library supports reading and writing of the following formats:
 - [a subset of PDB format](./format-pdb.html)
 - [DFTB+ general format](./format-gen.html)
 - [Gaussian external format](./format-ein.html)
+- [QCSchema JSON format](./format-qcschema.html)
diff --git a/fpm.toml b/fpm.toml
index 0586ad65..973895e9 100644
--- a/fpm.toml
+++ b/fpm.toml
@@ -6,3 +6,6 @@ author = ["Sebastian Ehlert"]
 copyright = "2020-2021 Sebastian Ehlert"
 description = "Modular computation tool chain library"
 keywords = ["computational-chemistry", "io"]
+
+[dependencies]
+json-fortran.git = "https://github.com/jacobwilliams/json-fortran.git"
diff --git a/include/mctc/defs.h b/include/mctc/defs.h
new file mode 100644
index 00000000..0e7925ca
--- /dev/null
+++ b/include/mctc/defs.h
@@ -0,0 +1,8 @@
+#ifndef mctc_defs_fh
+#define mctc_defs_fh
+
+#ifndef WITH_JSON
+#define WITH_JSON 1
+#endif
+
+#endif
diff --git a/man/mctc-convert.1.adoc b/man/mctc-convert.1.adoc
index 0d090cd0..23823ed9 100644
--- a/man/mctc-convert.1.adoc
+++ b/man/mctc-convert.1.adoc
@@ -26,6 +26,7 @@ Supported formats:
 - Protein Database files, only single files (pdb)
 - Connection table files, molfile (mol) and structure data format (sdf)
 - Gaussian's external program input (ein)
+- JSON input with `qcschema_molecule` or `qcschema_input` structure (json)
 
 
 == Options
diff --git a/meson.build b/meson.build
index 5c2000d3..3b4339f6 100644
--- a/meson.build
+++ b/meson.build
@@ -17,7 +17,7 @@ project(
   'fortran',
   version: '0.2.3',
   license: 'Apache-2.0',
-  meson_version: '>=0.53',
+  meson_version: '>=0.55',
   default_options: [
     'buildtype=debugoptimized',
     'default_library=both',
@@ -38,7 +38,11 @@ mctc_lib = library(
   meson.project_name(),
   sources: srcs,
   version: meson.project_version(),
+  include_directories: include_directories('include'),
   dependencies: lib_deps,
+  fortran_args: [
+    '-DWITH_JSON=@0@'.format(jsonfortran_dep.found() ? '1' : '0'),
+  ],
   install: install,
 )
 
diff --git a/meson_options.txt b/meson_options.txt
index 1bd87b7c..fc24d75d 100644
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -19,3 +19,11 @@ option(
   yield: true,
   description: 'use OpenMP parallelisation',
 )
+
+option(
+  'json',
+  type: 'feature',
+  value: 'auto',
+  yield: true,
+  description: 'support JSON input',
+)
diff --git a/src/mctc/CMakeLists.txt b/src/mctc/CMakeLists.txt
index e6cc698f..89bb8407 100644
--- a/src/mctc/CMakeLists.txt
+++ b/src/mctc/CMakeLists.txt
@@ -21,7 +21,7 @@ list(
   APPEND srcs
   "${dir}/env.f90"
   "${dir}/io.f90"
-  "${dir}/version.f90"
+  "${dir}/version.F90"
 )
 
 set(srcs "${srcs}" PARENT_SCOPE)
diff --git a/src/mctc/io/read.f90 b/src/mctc/io/read.f90
index e125f0fc..5d27d584 100644
--- a/src/mctc/io/read.f90
+++ b/src/mctc/io/read.f90
@@ -18,6 +18,7 @@ module mctc_io_read
    use mctc_io_read_ctfile, only : read_molfile, read_sdf
    use mctc_io_read_gaussian, only : read_gaussian_external
    use mctc_io_read_genformat, only : read_genformat
+   use mctc_io_read_qcschema, only : read_qcschema
    use mctc_io_read_pdb, only : read_pdb
    use mctc_io_read_turbomole, only : read_coord
    use mctc_io_read_vasp, only : read_vasp
@@ -143,6 +144,9 @@ subroutine get_structure_reader(reader, ftype)
    case(filetype%molfile)
       reader => read_molfile
 
+   case(filetype%qcschema)
+      reader => read_qcschema
+
    case(filetype%pdb)
       reader => read_pdb
 
diff --git a/src/mctc/io/read/CMakeLists.txt b/src/mctc/io/read/CMakeLists.txt
index 7ac512da..e8eb70eb 100644
--- a/src/mctc/io/read/CMakeLists.txt
+++ b/src/mctc/io/read/CMakeLists.txt
@@ -19,6 +19,7 @@ list(
   "${dir}/ctfile.f90"
   "${dir}/gaussian.f90"
   "${dir}/genformat.f90"
+  "${dir}/qcschema.F90"
   "${dir}/pdb.f90"
   "${dir}/turbomole.f90"
   "${dir}/vasp.f90"
diff --git a/src/mctc/io/read/meson.build b/src/mctc/io/read/meson.build
index b8629ee6..ef9e0407 100644
--- a/src/mctc/io/read/meson.build
+++ b/src/mctc/io/read/meson.build
@@ -16,6 +16,7 @@ srcs += files(
   'ctfile.f90',
   'gaussian.f90',
   'genformat.f90',
+  'qcschema.F90',
   'pdb.f90',
   'turbomole.f90',
   'vasp.f90',
diff --git a/src/mctc/io/read/qcschema.F90 b/src/mctc/io/read/qcschema.F90
new file mode 100644
index 00000000..893129a8
--- /dev/null
+++ b/src/mctc/io/read/qcschema.F90
@@ -0,0 +1,180 @@
+! This file is part of mctc-lib.
+!
+! Licensed under the Apache License, Version 2.0 (the "License");
+! you may not use this file except in compliance with the License.
+! You may obtain a copy of the License at
+!
+!     http://www.apache.org/licenses/LICENSE-2.0
+!
+! Unless required by applicable law or agreed to in writing, software
+! distributed under the License is distributed on an "AS IS" BASIS,
+! WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+! See the License for the specific language governing permissions and
+! limitations under the License.
+
+#include "mctc/defs.h"
+
+module mctc_io_read_qcschema
+   use mctc_env_accuracy, only : wp
+   use mctc_env_error, only : error_type, fatal_error
+   use mctc_io_structure, only : structure_type, new
+   use mctc_io_symbols, only : to_number, symbol_length
+   use mctc_io_utils, only : getline
+#if WITH_JSON
+   use json_value_module, only : json_core, json_value
+#endif
+   implicit none
+   private
+
+   public :: read_qcschema
+
+
+contains
+
+
+subroutine read_qcschema(self, unit, error)
+
+   !> Instance of the molecular structure data
+   type(structure_type), intent(out) :: self
+
+   !> File handle
+   integer, intent(in) :: unit
+
+   !> Error handling
+   type(error_type), allocatable, intent(out) :: error
+
+#if WITH_JSON
+   type(json_core) :: json
+   type(json_value), pointer :: root, val, child, array
+
+   integer :: stat, schema_version, charge, multiplicity, ibond
+   character(len=:), allocatable :: input, line, message, schema_name, comment
+   character(len=symbol_length), allocatable :: sym(:)
+   integer, allocatable :: bond(:, :), list(:)
+   real(wp), allocatable, target :: geo(:)
+   real(wp), pointer :: xyz(:, :)
+
+   stat = 0
+   input = ""
+   do
+      call getline(unit, line, stat)
+      if (stat /= 0) exit
+      input = input // line
+   end do
+
+   call json%deserialize(root, input)
+   if (json%failed()) then
+      call json%check_for_errors(error_msg=message)
+      call fatal_error(error, message)
+      call json%destroy(root)
+      return
+   end if
+   val => root
+
+   call json%get(val, "schema_version", schema_version, default=2)
+   call json%get(val, "schema_name", schema_name, default="qcschema_molecule")
+
+   if (schema_name /= "qcschema_molecule" .and. schema_name /= "qcschema_input" &
+      & .or. json%failed()) then
+      call fatal_error(error, "Invalid schema name '"//schema_name//"'")
+      call json%destroy(root)
+      return
+   end if
+
+   if (schema_name == "qcschema_input") then
+      select case(schema_version)
+      case(1)
+         call json%get(val, "molecule", child)
+      case default
+         call fatal_error(error, "Unsupported schema version for 'qcschema_input'")
+         call json%destroy(root)
+         return
+      end select
+      call json%get(child, "schema_version", schema_version, default=2)
+      call json%get(child, "schema_name", schema_name, default="qcschema_molecule")
+
+      if (schema_name /= "qcschema_molecule" .or. json%failed()) then
+         call fatal_error(error, "Invalid schema name '"//schema_name//"'")
+         call json%destroy(root)
+         return
+      end if
+
+      val => child
+   end if
+
+   select case(schema_version)
+   case(1)
+      call json%get(val, "molecule", child)
+   case(2)
+      child => val
+   case default
+      call fatal_error(error, "Unsupported schema version for 'qcschema_molecule'")
+      call json%destroy(root)
+      return
+   end select
+
+   call json%get(child, "symbols", sym)
+   if (.not.allocated(sym) .or. json%failed()) then
+      call fatal_error(error, "List of atomic symbols must be provided")
+      call json%destroy(root)
+      return
+   end if
+   call json%get(child, "geometry", geo)
+   if (.not.allocated(geo) .or. json%failed()) then
+      call fatal_error(error, "Cartesian coordinates must be provided")
+      call json%destroy(root)
+      return
+   end if
+
+   if (3*size(sym) /= size(geo)) then
+      call fatal_error(error, "Number of symbols and coordinate triples must match")
+      call json%destroy(root)
+      return
+   end if
+
+   call json%get(child, "comment", comment, default="")
+   call json%get(child, "molecular_charge", charge, default=0)
+   call json%get(child, "molecular_multiplicity", multiplicity, default=1)
+
+   if (json%failed()) then
+      call json%check_for_errors(error_msg=message)
+      call fatal_error(error, message)
+      call json%destroy(root)
+      return
+   end if
+
+   call json%get_child(child, "connectivity", array)
+   if (associated(array)) then
+      allocate(bond(3, json%count(array)))
+      do ibond = 1, size(bond, 2)
+         call json%get_child(array, ibond, child)
+         call json%get(child, "", list)
+         if (allocated(list)) then
+            bond(:, ibond) = [list(1)+1, list(2)+1, list(3)]
+         end if
+      end do
+
+      if (json%failed()) then
+         call json%check_for_errors(error_msg=message)
+         call fatal_error(error, message)
+         call json%destroy(root)
+         return
+      end if
+   end if
+
+   xyz(1:3, 1:size(geo)/3) => geo
+   call new(self, sym, xyz, charge=real(charge, wp), uhf=multiplicity-1)
+   if (len(comment) > 0) self%comment = comment
+   if (allocated(bond)) then
+      self%nbd = size(bond, 2)
+      call move_alloc(bond, self%bond)
+   end if
+
+   call json%destroy(root)
+#else
+   call fatal_error(error, "JSON support not enabled")
+#endif
+end subroutine read_qcschema
+
+
+end module mctc_io_read_qcschema
diff --git a/src/mctc/meson.build b/src/mctc/meson.build
index 2653b243..d1e35b02 100644
--- a/src/mctc/meson.build
+++ b/src/mctc/meson.build
@@ -18,5 +18,5 @@ subdir('io')
 srcs += files(
   'env.f90',
   'io.f90',
-  'version.f90',
+  'version.F90',
 )
diff --git a/src/mctc/version.f90 b/src/mctc/version.F90
similarity index 77%
rename from src/mctc/version.f90
rename to src/mctc/version.F90
index d9327ce7..5618b636 100644
--- a/src/mctc/version.f90
+++ b/src/mctc/version.F90
@@ -12,12 +12,14 @@
 ! See the License for the specific language governing permissions and
 ! limitations under the License.
 
+#include "mctc/defs.h"
+
 module mctc_version
    implicit none
    private
 
    public :: mctc_version_string, mctc_version_compact
-   public :: get_mctc_version
+   public :: get_mctc_version, get_mctc_feature
 
 
    !> String representation of the mctc-lib version
@@ -27,6 +29,10 @@ module mctc_version
    integer, parameter :: mctc_version_compact(3) = [0, 2, 3]
 
 
+   !> With support for JSON
+   logical, parameter :: mctc_with_json = 0 /= WITH_JSON
+
+
 contains
 
 
@@ -61,4 +67,22 @@ pure subroutine get_mctc_version(major, minor, patch, string)
 end subroutine get_mctc_version
 
 
+pure function get_mctc_feature(feature) result(has_feature)
+
+   !> Feature name
+   character(len=*), intent(in) :: feature
+
+   !> Whether the feature is enabled
+   logical :: has_feature
+
+   select case(feature)
+   case("json")
+      has_feature = mctc_with_json
+   case default
+      has_feature = .false.
+   end select
+
+end function get_mctc_feature
+
+
 end module mctc_version
diff --git a/subprojects/.gitignore b/subprojects/.gitignore
new file mode 100644
index 00000000..3daff2f5
--- /dev/null
+++ b/subprojects/.gitignore
@@ -0,0 +1,2 @@
+/packagecache/
+/json-fortran-*/
diff --git a/subprojects/json-fortran-8.2.5.wrap b/subprojects/json-fortran-8.2.5.wrap
new file mode 100644
index 00000000..3a8bf523
--- /dev/null
+++ b/subprojects/json-fortran-8.2.5.wrap
@@ -0,0 +1,8 @@
+[wrap-file]
+directory = json-fortran-8.2.5
+
+source_url = https://github.com/jacobwilliams/json-fortran/archive/refs/tags/8.2.5.tar.gz
+source_filename = 8.2.5.tar.gz
+source_hash = 16eec827f64340c226ba9a8463f001901d469bc400a1e88b849f258f9ef0d100
+
+patch_directory = json-fortran-8.2.5
diff --git a/subprojects/packagefiles/json-fortran-8.2.5/meson.build b/subprojects/packagefiles/json-fortran-8.2.5/meson.build
new file mode 100644
index 00000000..2dcadd39
--- /dev/null
+++ b/subprojects/packagefiles/json-fortran-8.2.5/meson.build
@@ -0,0 +1,28 @@
+project(
+  'jsonfortran',
+  'Fortran',
+  version: files('.VERSION'),
+)
+
+jsonfortran_lib = library(
+  meson.project_name(),
+  sources: files(
+    'src/json_kinds.F90',
+    'src/json_parameters.F90',
+    'src/json_string_utilities.F90',
+    'src/json_value_module.F90',
+    'src/json_file_module.F90',
+    'src/json_module.F90',
+  ),
+  include_directories: include_directories('src'),
+)
+
+jsonfortran_dep = declare_dependency(
+  link_with: jsonfortran_lib,
+  include_directories: jsonfortran_lib.private_dir_include(),
+)
+
+install_data(
+  'LICENSE',
+  install_dir: get_option('datadir')/'licenses'/'mctc-lib'/meson.project_name()
+)
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index a4b6ac59..3e1547f3 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -20,6 +20,7 @@ set(
   "read-ctfile"
   "read-gaussian"
   "read-genformat"
+  "read-qcschema"
   "read-pdb"
   "read-turbomole"
   "read-vasp"
diff --git a/test/main.f90 b/test/main.f90
index c3058ddb..21e7f12e 100644
--- a/test/main.f90
+++ b/test/main.f90
@@ -23,6 +23,7 @@ program tester
    use test_read_ctfile, only : collect_read_ctfile
    use test_read_gaussian, only : collect_read_gaussian
    use test_read_genformat, only : collect_read_genformat
+   use test_read_qcschema, only : collect_read_qcschema
    use test_read_pdb, only : collect_read_pdb
    use test_read_turbomole, only : collect_read_turbomole
    use test_read_vasp, only : collect_read_vasp
@@ -51,6 +52,7 @@ program tester
       & new_testsuite("read-ctfile", collect_read_ctfile), &
       & new_testsuite("read-gaussian", collect_read_gaussian), &
       & new_testsuite("read-genformat", collect_read_genformat), &
+      & new_testsuite("read-qcschema", collect_read_qcschema), &
       & new_testsuite("read-pdb", collect_read_pdb), &
       & new_testsuite("read-turbomole", collect_read_turbomole), &
       & new_testsuite("read-vasp", collect_read_vasp), &
diff --git a/test/meson.build b/test/meson.build
index 7edc9f34..f4a6ff02 100644
--- a/test/meson.build
+++ b/test/meson.build
@@ -18,6 +18,7 @@ tests = [
   'read-ctfile',
   'read-gaussian',
   'read-genformat',
+  'read-qcschema',
   'read-pdb',
   'read-turbomole',
   'read-vasp',
diff --git a/test/test_read.f90 b/test/test_read.f90
index ecd6e655..b2a9ee07 100644
--- a/test/test_read.f90
+++ b/test/test_read.f90
@@ -18,6 +18,7 @@ module test_read
    use mctc_io_read
    use mctc_io_structure, only : structure_type
    use mctc_io_filetype, only : get_filetype
+   use mctc_version, only : get_mctc_feature
    implicit none
    private
 
@@ -37,6 +38,7 @@ subroutine collect_read(testsuite)
       & new_unittest("valid-mol", test_mol), &
       & new_unittest("valid-sdf", test_sdf), &
       & new_unittest("valid-gen", test_gen), &
+      & new_unittest("valid-qcschema", test_qcschema, should_fail=.not.get_mctc_feature("json")), &
       & new_unittest("valid-pdb", test_pdb), &
       & new_unittest("valid-vasp", test_vasp), &
       & new_unittest("valid-coord", test_coord), &
@@ -417,6 +419,96 @@ subroutine test_xyz(error)
 end subroutine test_xyz
 
 
+subroutine test_qcschema(error)
+
+   !> Error handling
+   type(error_type), allocatable, intent(out) :: error
+
+   type(structure_type) :: struc
+   character(len=:), allocatable :: name
+   integer :: unit
+
+   name = get_name() // ".json"
+
+   open(file=name, newunit=unit)
+   write(unit, '(a)') &
+     '{', &
+     '  "schema_version": 2,', &
+     '  "schema_name": "qcschema_molecule",', &
+     '  "provenance": {', &
+     '    "creator": "mctc-lib",', &
+     '    "version": "0.2.3",', &
+     '    "routine": "mctc_io_write_qcschema::write_qcschema"', &
+     '  },', &
+     '  "symbols": [', &
+     '    "C", "N", "C", "N", "C", "C", "C", "O", "N", "C", "O", "N",', &
+     '    "C", "C", "H", "H", "H", "H", "H", "H", "H", "H", "H", "H"', &
+     '  ],', &
+     '  "geometry": [', &
+     '     2.0280536328008760E+00, 9.2407587256767454E-02,-1.4305223630546618E-01,', &
+     '     4.7502035191684326E+00, 2.3810543955731494E-02,-1.4324120887654343E-01,', &
+     '     6.3343605825088858E+00, 2.0709504064354083E+00,-1.4229634602115726E-01,', &
+     '     8.7286430580574415E+00, 1.3800666865770403E+00,-1.4267429116331171E-01,', &
+     '     8.6532430021976250E+00,-1.1931728137816557E+00,-1.4229634602115726E-01,', &
+     '     6.2385514889727283E+00,-2.0836115686975827E+00,-1.4210737345008001E-01,', &
+     '     5.6327054260991156E+00,-4.6995588701197342E+00,-1.3946175745499875E-01,', &
+     '     3.4493163398727531E+00,-5.4809604515240968E+00,-1.4324120887654343E-01,', &
+     '     7.7750874644017181E+00,-6.2442206661050452E+00,-1.3114696432760045E-01,', &
+     '     1.0302217657417570E+01,-5.3974345751079591E+00,-1.3681614145991747E-01,', &
+     '     1.2074024483837716E+01,-6.9158291837135346E+00,-1.3662716888884024E-01,', &
+     '     1.0700382864677302E+01,-2.7907469296685923E+00,-1.4154045573684831E-01,', &
+     '     1.3246032369658721E+01,-1.7697281281382971E+00,-1.4210737345008001E-01,', &
+     '     7.4088586216540389E+00,-8.9590006222005893E+00,-1.1640710378357619E-01,', &
+     '     1.3870586717068980E+00, 2.0558326007492296E+00,-1.4172942830792554E-01,', &
+     '     1.3462405963542154E+00,-8.6360464982295970E-01, 1.5560001502499454E+00,', &
+     '     1.3462405963542154E+00,-8.6133697897003281E-01,-1.8434274308584184E+00,', &
+     '     5.6559490523416152E+00, 4.0016831651315083E+00,-1.4135148316577109E-01,', &
+     '     1.4674287061860456E+01,-3.2622334945062916E+00,-1.4343018144762065E-01,', &
+     '     1.3508893216027154E+01,-6.0811373372653921E-01, 1.5490081651200875E+00,', &
+     '     1.3507759380600691E+01,-6.0622400801576681E-01,-1.8320890765937843E+00,', &
+     '     5.4140641613627567E+00,-9.4924701903516215E+00,-1.1017100893802745E-01,', &
+     '     8.3191394965330758E+00,-9.7494728870166600E+00, 1.5654487788038070E+00,', &
+     '     8.3151710725404531E+00,-9.7685591166954602E+00,-1.7910820286700244E+00', &
+     '  ],', &
+     '  "molecular_charge": 0,', &
+     '  "connectivity": [', &
+     '    [ 0, 1, 1],', &
+     '    [ 1, 2, 4],', &
+     '    [ 2, 3, 4],', &
+     '    [ 3, 4, 4],', &
+     '    [ 1, 5, 1],', &
+     '    [ 4, 5, 4],', &
+     '    [ 5, 6, 1],', &
+     '    [ 6, 7, 2],', &
+     '    [ 6, 8, 1],', &
+     '    [ 8, 9, 1],', &
+     '    [ 9,10, 2],', &
+     '    [ 4,11, 1],', &
+     '    [ 9,11, 1],', &
+     '    [11,12, 1],', &
+     '    [ 8,13, 1],', &
+     '    [ 0,14, 1],', &
+     '    [ 0,15, 1],', &
+     '    [ 0,16, 1],', &
+     '    [ 2,17, 1],', &
+     '    [12,18, 1],', &
+     '    [12,19, 1],', &
+     '    [12,20, 1],', &
+     '    [13,21, 1],', &
+     '    [13,22, 1],', &
+     '    [13,23, 1]', &
+     '  ]', &
+     '}'
+   close(unit)
+
+   call read_structure(struc, name, error)
+
+   open(file=name, newunit=unit)
+   close(unit, status='delete')
+
+end subroutine test_qcschema
+
+
 function get_name() result(name)
 
    character(len=18) :: name
diff --git a/test/test_read_qcschema.f90 b/test/test_read_qcschema.f90
new file mode 100644
index 00000000..54834588
--- /dev/null
+++ b/test/test_read_qcschema.f90
@@ -0,0 +1,477 @@
+! This file is part of mctc-lib.
+!
+! Licensed under the Apache License, Version 2.0 (the "License");
+! you may not use this file except in compliance with the License.
+! You may obtain a copy of the License at
+!
+!     http://www.apache.org/licenses/LICENSE-2.0
+!
+! Unless required by applicable law or agreed to in writing, software
+! distributed under the License is distributed on an "AS IS" BASIS,
+! WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+! See the License for the specific language governing permissions and
+! limitations under the License.
+
+module test_read_qcschema
+   use mctc_env_testing, only : new_unittest, unittest_type, error_type, check
+   use mctc_io_read_qcschema
+   use mctc_io_structure
+   use mctc_version, only : get_mctc_feature
+   implicit none
+   private
+
+   public :: collect_read_qcschema
+
+
+contains
+
+
+!> Collect all exported unit tests
+subroutine collect_read_qcschema(testsuite)
+
+   !> Collection of tests
+   type(unittest_type), allocatable, intent(out) :: testsuite(:)
+
+   logical :: with_json
+
+   with_json = get_mctc_feature("json")
+
+   testsuite = [ &
+      & new_unittest("valid1-qcschema", test_valid1_qcschema, should_fail=.not.with_json), &
+      & new_unittest("valid2-qcschema", test_valid2_qcschema, should_fail=.not.with_json), &
+      & new_unittest("invalid1-qcschema", test_invalid1_qcschema, should_fail=.true.), &
+      & new_unittest("invalid2-qcschema", test_invalid2_qcschema, should_fail=.true.), &
+      & new_unittest("invalid3-qcschema", test_invalid3_qcschema, should_fail=.true.), &
+      & new_unittest("invalid4-qcschema", test_invalid4_qcschema, should_fail=.true.), &
+      & new_unittest("invalid5-qcschema", test_invalid5_qcschema, should_fail=.true.), &
+      & new_unittest("invalid6-qcschema", test_invalid6_qcschema, should_fail=.true.) &
+      & ]
+
+end subroutine collect_read_qcschema
+
+
+subroutine test_valid1_qcschema(error)
+
+   !> Error handling
+   type(error_type), allocatable, intent(out) :: error
+
+   type(structure_type) :: struc
+   integer :: unit
+
+   open(status='scratch', newunit=unit)
+   write(unit, '(a)') &
+      '{', &
+      '  "schema_version": 1,', &
+      '  "molecule": {', &
+      '    "geometry": [', &
+      '      0.0,  0.0000, -0.1294,', &
+      '      0.0, -1.4941,  1.0274,', &
+      '      0.0,  1.4941,  1.0274', &
+      '    ],', &
+      '    "symbols": ["O", "H", "H"],', &
+      '    "comment": "Water molecule"', &
+      '  }', &
+      '}'
+   rewind(unit)
+
+   call read_qcschema(struc, unit, error)
+   close(unit)
+   if (allocated(error)) return
+
+   call check(error, allocated(struc%comment), "Comment line should be preserved")
+   if (allocated(error)) return
+   call check(error, struc%comment, "Water molecule")
+   if (allocated(error)) return
+   call check(error, struc%nat, 3, "Number of atoms does not match")
+   if (allocated(error)) return
+   call check(error, struc%nid, 2, "Number of species does not match")
+   if (allocated(error)) return
+
+end subroutine test_valid1_qcschema
+
+
+subroutine test_valid2_qcschema(error)
+
+   !> Error handling
+   type(error_type), allocatable, intent(out) :: error
+
+   type(structure_type) :: struc
+   integer :: unit
+
+   open(status='scratch', newunit=unit)
+   write(unit, '(a)') &
+      '{', &
+      '  "schema_version": 1,', &
+      '  "schema_name": "qcschema_input",', &
+      '  "driver": "energy",', &
+      '  "model": {', &
+      '    "method": "xtb",', &
+      '    "basis": null', &
+      '  },', &
+      '  "molecule": {', &
+      '    "schema_version": 2,', &
+      '    "schema_name": "qcschema_molecule",', &
+      '    "provenance": {', &
+      '      "creator": "mctc-lib",', &
+      '      "version": "0.2.3",', &
+      '      "routine": "mctc_io_write_qcschema::write_qcschema"', &
+      '    },', &
+      '    "symbols": [', &
+      '      "C", "C", "C", "C", "C", "C", "H", "H", "H", "H", "H", "H",', &
+      '      "H", "H", "H", "H", "H", "C", "C", "C", "C", "C", "C", "H",', &
+      '      "H", "H", "H", "H", "H", "H", "H", "H", "H", "H", "H", "H",', &
+      '      "H", "H"', &
+      '    ],', &
+      '    "geometry": [', &
+      '       1.1910941154998063E+00, 8.0445623507578545E-01, 0.0000000000000000E+00,', &
+      '       3.6246828858324265E+00,-7.2565467293657882E-01, 0.0000000000000000E+00,', &
+      '       6.0068711168320394E+00, 8.8306882464391478E-01, 0.0000000000000000E+00,', &
+      '       8.4393260517381972E+00,-6.4779797365275837E-01, 0.0000000000000000E+00,', &
+      '       1.0824537843875046E+01, 9.5827990793265394E-01, 0.0000000000000000E+00,', &
+      '       1.3237906549102401E+01,-5.9564154403544178E-01, 0.0000000000000000E+00,', &
+      '       1.4916738870552548E+01, 5.9753126974621407E-01, 0.0000000000000000E+00,', &
+      '       1.3341085572910570E+01,-1.8126249017728293E+00,-1.6605019820556557E+00,', &
+      '       1.3341085572910570E+01,-1.8126249017728293E+00, 1.6605019820556557E+00,', &
+      '       1.0802428053059009E+01, 2.2054988770423987E+00,-1.6484077375067128E+00,', &
+      '       1.0802428053059009E+01, 2.2054988770423987E+00, 1.6484077375067128E+00,', &
+      '       8.4618137876963875E+00,-1.8965287233311212E+00, 1.6491636277910218E+00,', &
+      '       8.4618137876963875E+00,-1.8965287233311212E+00,-1.6491636277910218E+00,', &
+      '       5.9874069420110843E+00, 2.1312326566090456E+00,-1.6493526003620989E+00,', &
+      '       5.9874069420110843E+00, 2.1312326566090456E+00, 1.6493526003620989E+00,', &
+      '       3.6452808960798451E+00,-1.9740074774727869E+00, 1.6491636277910218E+00,', &
+      '       3.6452808960798451E+00,-1.9740074774727869E+00,-1.6491636277910218E+00,', &
+      '      -1.1910941154998063E+00,-8.0445623507578545E-01, 0.0000000000000000E+00,', &
+      '      -3.6246828858324265E+00, 7.2565467293657882E-01, 0.0000000000000000E+00,', &
+      '      -6.0068711168320394E+00,-8.8306882464391478E-01, 0.0000000000000000E+00,', &
+      '      -8.4393260517381972E+00, 6.4779797365275837E-01, 0.0000000000000000E+00,', &
+      '      -1.0824537843875046E+01,-9.5827990793265394E-01, 0.0000000000000000E+00,', &
+      '      -1.3237906549102401E+01, 5.9564154403544178E-01, 0.0000000000000000E+00,', &
+      '      -1.4916738870552548E+01,-5.9753126974621407E-01, 0.0000000000000000E+00,', &
+      '      -1.3341085572910570E+01, 1.8126249017728293E+00, 1.6605019820556557E+00,', &
+      '      -1.3341085572910570E+01, 1.8126249017728293E+00,-1.6605019820556557E+00,', &
+      '      -1.0802428053059009E+01,-2.2054988770423987E+00,-1.6484077375067128E+00,', &
+      '      -1.0802428053059009E+01,-2.2054988770423987E+00, 1.6484077375067128E+00,', &
+      '      -8.4618137876963875E+00, 1.8965287233311212E+00, 1.6491636277910218E+00,', &
+      '      -8.4618137876963875E+00, 1.8965287233311212E+00,-1.6491636277910218E+00,', &
+      '      -5.9874069420110843E+00,-2.1312326566090456E+00,-1.6493526003620989E+00,', &
+      '      -5.9874069420110843E+00,-2.1312326566090456E+00, 1.6493526003620989E+00,', &
+      '      -3.6452808960798451E+00, 1.9740074774727869E+00,-1.6491636277910218E+00,', &
+      '      -3.6452808960798451E+00, 1.9740074774727869E+00, 1.6491636277910218E+00,', &
+      '      -1.1706850778234652E+00,-2.0526200670409165E+00, 1.6491636277910218E+00,', &
+      '      -1.1706850778234652E+00,-2.0526200670409165E+00,-1.6491636277910218E+00,', &
+      '       1.1706850778234652E+00, 2.0526200670409165E+00,-1.6491636277910218E+00,', &
+      '       1.1706850778234652E+00, 2.0526200670409165E+00, 1.6491636277910218E+00', &
+      '    ],', &
+      '    "molecular_charge": 0,', &
+      '    "connectivity": [', &
+      '      [ 0, 1, 1],  [ 1, 2, 1],  [ 2, 3, 1],  [ 3, 4, 1],  [ 4, 5, 1],', &
+      '      [ 5, 6, 1],  [ 5, 7, 1],  [ 5, 8, 1],  [ 4, 9, 1],  [ 4,10, 1],', &
+      '      [ 3,11, 1],  [ 3,12, 1],  [ 2,13, 1],  [ 2,14, 1],  [ 1,15, 1],', &
+      '      [ 1,16, 1],  [ 0,17, 1],  [17,18, 1],  [18,19, 1],  [19,20, 1],', &
+      '      [20,21, 1],  [21,22, 1],  [22,23, 1],  [22,24, 1],  [22,25, 1],', &
+      '      [21,26, 1],  [21,27, 1],  [20,28, 1],  [20,29, 1],  [19,30, 1],', &
+      '      [19,31, 1],  [18,32, 1],  [18,33, 1],  [17,34, 1],  [17,35, 1],', &
+      '      [ 0,36, 1],  [ 0,37, 1]', &
+      '    ]', &
+      '  }', &
+      '}'
+   rewind(unit)
+
+   call read_qcschema(struc, unit, error)
+   close(unit)
+   if (allocated(error)) return
+
+   call check(error, .not.allocated(struc%comment), "Empty comment line should not be saved")
+   if (allocated(error)) return
+   call check(error, struc%nat, 38, "Number of atoms does not match")
+   if (allocated(error)) return
+   call check(error, struc%nid, 2, "Number of species does not match")
+   if (allocated(error)) return
+
+end subroutine test_valid2_qcschema
+
+
+subroutine test_valid4_qcschema(error)
+
+   !> Error handling
+   type(error_type), allocatable, intent(out) :: error
+
+   type(structure_type) :: struc
+   integer :: unit
+
+   open(status='scratch', newunit=unit)
+   write(unit, '(a)') &
+      "3", &
+      "WATER27, H2O", &
+      "O     1.1847029    1.1150792   -0.0344641 ", &
+      "H     0.4939088    0.9563767    0.6340089 ", &
+      "H     2.0242676    1.0811246    0.4301417 ", &
+      "3", &
+      "WATER27, H2O", &
+      "O    -1.1469443    0.0697649    1.1470196 ", &
+      "H    -1.2798308   -0.5232169    1.8902833 ", &
+      "H    -1.0641398   -0.4956693    0.3569250 ", &
+      "3", &
+      "WATER27, H2O", &
+      "O    -0.1633508   -1.0289346   -1.2401808 ", &
+      "H     0.4914771   -0.3248733   -1.0784838 ", &
+      "H    -0.5400907   -0.8496512   -2.1052499 "
+   rewind(unit)
+
+   call read_qcschema(struc, unit, error)
+   if (.not.allocated(error)) then
+      call read_qcschema(struc, unit, error)
+   end if
+   close(unit)
+   if (allocated(error)) return
+
+   call check(error, struc%nat, 3, "Number of atoms does not match")
+   if (allocated(error)) return
+   call check(error, struc%nid, 2, "Number of species does not match")
+   if (allocated(error)) return
+
+end subroutine test_valid4_qcschema
+
+
+subroutine test_valid5_qcschema(error)
+
+   !> Error handling
+   type(error_type), allocatable, intent(out) :: error
+
+   type(structure_type) :: struc
+   integer :: unit
+
+   open(status='scratch', newunit=unit)
+   write(unit, '(a)') &
+      "3", &
+      "WATER27, H2O", &
+      "8     1.1847029    1.1150792   -0.0344641 ", &
+      "1     0.4939088    0.9563767    0.6340089 ", &
+      "1     2.0242676    1.0811246    0.4301417 ", &
+      "3", &
+      "WATER27, H2O", &
+      "8    -1.1469443    0.0697649    1.1470196 ", &
+      "1    -1.2798308   -0.5232169    1.8902833 ", &
+      "1    -1.0641398   -0.4956693    0.3569250 "
+   rewind(unit)
+
+   call read_qcschema(struc, unit, error)
+   if (.not.allocated(error)) then
+      call read_qcschema(struc, unit, error)
+   end if
+   close(unit)
+   if (allocated(error)) return
+
+   call check(error, struc%nat, 3, "Number of atoms does not match")
+   if (allocated(error)) return
+   call check(error, struc%nid, 2, "Number of species does not match")
+   if (allocated(error)) return
+
+end subroutine test_valid5_qcschema
+
+
+subroutine test_invalid1_qcschema(error)
+
+   !> Error handling
+   type(error_type), allocatable, intent(out) :: error
+
+   type(structure_type) :: struc
+   integer :: unit
+
+   open(status='scratch', newunit=unit)
+   write(unit, '(a)') &
+      '{', &
+      '  "schema_version": 2,', &
+      '  "schema_name": "qcschema_molecule",', &
+      '  "molecule": {', &
+      '    "geometry": [', &
+      '      0.0,  0.0000, -0.1294,', &
+      '      0.0, -1.4941,  1.0274,', &
+      '      0.0,  1.4941,  1.0274', &
+      '    ],', &
+      '    "symbols": ["O", "H", "H"],', &
+      '    "comment": "Water molecule"', &
+      '  }', &
+      '}'
+   rewind(unit)
+
+   call read_qcschema(struc, unit, error)
+   close(unit)
+   if (allocated(error)) return
+
+end subroutine test_invalid1_qcschema
+
+
+subroutine test_invalid2_qcschema(error)
+
+   !> Error handling
+   type(error_type), allocatable, intent(out) :: error
+
+   type(structure_type) :: struc
+   integer :: unit
+
+   open(status='scratch', newunit=unit)
+   write(unit, '(a)') &
+      '{', &
+      '  "schema_version": 0,', &
+      '  "schema_name": "qcschema_molecule",', &
+      '  "molecule": {', &
+      '    "geometry": [', &
+      '      0.0,  0.0000, -0.1294,', &
+      '      0.0, -1.4941,  1.0274,', &
+      '      0.0,  1.4941,  1.0274', &
+      '    ],', &
+      '    "symbols": ["O", "H", "H"],', &
+      '    "comment": "Water molecule"', &
+      '  }', &
+      '}'
+   rewind(unit)
+
+   call read_qcschema(struc, unit, error)
+   close(unit)
+   if (allocated(error)) return
+
+end subroutine test_invalid2_qcschema
+
+
+subroutine test_invalid3_qcschema(error)
+
+   !> Error handling
+   type(error_type), allocatable, intent(out) :: error
+
+   type(structure_type) :: struc
+   integer :: unit
+
+   open(status='scratch', newunit=unit)
+   write(unit, '(a)') &
+      '{', &
+      '  "schema_version": 1,', &
+      '  "schema_name": "qcschema_molecule",', &
+      '  "molecule": {', &
+      '    "geometry": [', &
+      '      0.0,  0.0000, -0.1294,', &
+      '      0.0, -1.4941,  1.0274,', &
+      '      0.0,  1.4941,  1.0274', &
+      '    ],', &
+      '    "symbols": ["O", "H", "H", "H"],', &
+      '  }', &
+      '}'
+   rewind(unit)
+
+   call read_qcschema(struc, unit, error)
+   close(unit)
+   if (allocated(error)) return
+
+end subroutine test_invalid3_qcschema
+
+
+subroutine test_invalid4_qcschema(error)
+
+   !> Error handling
+   type(error_type), allocatable, intent(out) :: error
+
+   type(structure_type) :: struc
+   integer :: unit
+
+   open(status='scratch', newunit=unit)
+   write(unit, '(a)') &
+      '{', &
+      '  "schema_version": 1,', &
+      '  "schema_name": "qcschema_molecule",', &
+      '  "molecule": {', &
+      '    "geometry": [', &
+      '      0.0,  0.0000, -0.1294,', &
+      '      0.0, -1.4941,  1.0274,', &
+      '      0.0,  1.4941,  1.0274', &
+      '    ],', &
+      '    "atomic_numbers": [8, 1, 1],', &
+      '  }', &
+      '}'
+   rewind(unit)
+
+   call read_qcschema(struc, unit, error)
+   close(unit)
+   if (allocated(error)) return
+
+end subroutine test_invalid4_qcschema
+
+
+subroutine test_invalid5_qcschema(error)
+
+   !> Error handling
+   type(error_type), allocatable, intent(out) :: error
+
+   type(structure_type) :: struc
+   integer :: unit
+
+   open(status='scratch', newunit=unit)
+   write(unit, '(a)') &
+      '{', &
+      '  "schema_version": 1,', &
+      '  "schema_name": "qcschema_molecule",', &
+      '  "molecule": {', &
+      '    "geometry": [', &
+      '      0.0,  0.0000, -0.1294,', &
+      '      0.0, -1.4941,  1.0274,'
+   rewind(unit)
+
+   call read_qcschema(struc, unit, error)
+   close(unit)
+   if (allocated(error)) return
+
+end subroutine test_invalid5_qcschema
+
+
+subroutine test_invalid6_qcschema(error)
+
+   !> Error handling
+   type(error_type), allocatable, intent(out) :: error
+
+   type(structure_type) :: struc
+   integer :: unit
+
+   open(status='scratch', newunit=unit)
+   write(unit, '(a)') &
+      '{', &
+      '  "chemical json": 0,', &
+      '  "name": "ethane",', &
+      '  "inchi": "1/C2H6/c1-2/h1-2H3",', &
+      '  "formula": "C 2 H 6",', &
+      '  "atoms": {', &
+      '    "elements": {', &
+      '      "number": [  1,   6,   1,   1,   6,   1,   1,   1 ]', &
+      '    },', &
+      '    "coords": {', &
+      '      "3d": [  1.185080, -0.003838,  0.987524,', &
+      '               0.751621, -0.022441, -0.020839,', &
+      '               1.166929,  0.833015, -0.569312,', &
+      '               1.115519, -0.932892, -0.514525,', &
+      '              -0.751587,  0.022496,  0.020891,', &
+      '              -1.166882, -0.833372,  0.568699,', &
+      '              -1.115691,  0.932608,  0.515082,', &
+      '              -1.184988,  0.004424, -0.987522 ]', &
+      '    }', &
+      '  },', &
+      '  "bonds": {', &
+      '    "connections": {', &
+      '      "index": [ 0, 1,', &
+      '                 1, 2,', &
+      '                 1, 3,', &
+      '                 1, 4,', &
+      '                 4, 5,', &
+      '                 4, 6,', &
+      '                 4, 7 ]', &
+      '    },', &
+      '    "order": [ 1, 1, 1, 1, 1, 1, 1 ]', &
+      '  }', &
+      '}'
+   rewind(unit)
+
+   call read_qcschema(struc, unit, error)
+   close(unit)
+   if (allocated(error)) return
+
+end subroutine test_invalid6_qcschema
+
+
+end module test_read_qcschema
diff --git a/test/test_write.f90 b/test/test_write.f90
index 97597edc..f50e9592 100644
--- a/test/test_write.f90
+++ b/test/test_write.f90
@@ -18,6 +18,7 @@ module test_write
    use mctc_io_write
    use mctc_io_read
    use mctc_io_structure, only : structure_type
+   use mctc_version, only : get_mctc_feature
    use testsuite_structure, only : get_structure
    implicit none
    private
@@ -38,6 +39,7 @@ subroutine collect_write(testsuite)
       & new_unittest("valid-mol", test_mol), &
       & new_unittest("valid-sdf", test_sdf), &
       & new_unittest("valid-gen", test_gen), &
+      & new_unittest("valid-qcschema", test_qcschema, should_fail=.not.get_mctc_feature("json")), &
       & new_unittest("valid-pdb", test_pdb), &
       & new_unittest("valid-vasp", test_vasp), &
       & new_unittest("valid-coord", test_coord), &
@@ -215,6 +217,30 @@ subroutine test_xyz(error)
 end subroutine test_xyz
 
 
+subroutine test_qcschema(error)
+
+   !> Error handling
+   type(error_type), allocatable, intent(out) :: error
+
+   type(structure_type) :: struc
+   character(len=:), allocatable :: name
+   integer :: unit
+
+   name = get_name() // ".json"
+
+   call get_structure(struc, "mindless05")
+
+   call write_structure(struc, name, error)
+   if (.not.allocated(error)) then
+      call read_structure(struc, name, error)
+   end if
+
+   open(file=name, newunit=unit)
+   close(unit, status='delete')
+
+end subroutine test_qcschema
+
+
 function get_name() result(name)
 
    character(len=18) :: name