diff --git a/cmake/Modules/Tools.cmake b/cmake/Modules/Tools.cmake
index 94e077d51e..e37e262bfe 100644
--- a/cmake/Modules/Tools.cmake
+++ b/cmake/Modules/Tools.cmake
@@ -6,6 +6,10 @@ if(BUILD_TOOLS)
   add_executable(stl_bin2txt ${LAMMPS_TOOLS_DIR}/stl_bin2txt.cpp)
   install(TARGETS stl_bin2txt DESTINATION ${CMAKE_INSTALL_BINDIR})
 
+  add_executable(reformat-json ${LAMMPS_TOOLS_DIR}/json/reformat-json.cpp)
+  target_include_directories(reformat-json PRIVATE ${LAMMPS_SOURCE_DIR})
+  install(TARGETS reformat-json DESTINATION ${CMAKE_INSTALL_BINDIR})
+
   include(CheckGeneratorSupport)
   if(CMAKE_GENERATOR_SUPPORT_FORTRAN)
     include(CheckLanguage)
diff --git a/doc/src/Tools.rst b/doc/src/Tools.rst
index 2ace39c500..bb59f72fb3 100644
--- a/doc/src/Tools.rst
+++ b/doc/src/Tools.rst
@@ -489,6 +489,29 @@ files even if the LAMMPS sources are not locally available. Example:
 
    check-jsonschema --schemafile https://download.lammps.org/json/molecule-schema.json tip3p.json
 
+JSON file format normalization
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+There are extensions to the strict JSON format that allow for comments
+or ignore additional (dangling) commas. The ``reformat-json.cpp`` tool
+will read JSON files in relaxed format, but write it out in strict format.
+It is also possible to change the level of indentation from -1 (all data
+one long line) to any positive integer value.  The original file will be
+backed up (.bak added to file name) and then overwritten.
+
+Manual compilation (it will be automatically included in the CMake build
+if building tools is requested during CMake configuration):
+
+.. code-block:: sh
+
+   g++ -I <path/to/lammps/src> -o reformat-json reformat-json.cpp
+
+Usage:
+
+.. parsed-literal::
+
+   reformat-json <indent-width> <json-file-1> [<json-file-2> ...]
+
 ----------
 
 .. _kate:
diff --git a/tools/json/README.md b/tools/json/README.md
index 135cdb8fb4..a4b2a11f1f 100644
--- a/tools/json/README.md
+++ b/tools/json/README.md
@@ -40,6 +40,22 @@ ok -- validation done
 ```
 Otherwise details about the non-conforming fields are given.
 
+# JSON file format normalization
+
+There are extensions to the strict JSON format that allow for comments
+or ignore additional (dangling) commas. The ``reformat-json.cpp`` tool
+will read JSON files in relaxed format, but write it out in strict format.
+It is also possible to change the level of indentation from -1 (all data
+one long line) to any positive integer value.  The original file will be
+backed up (.bak added to file name) and then overwritten.
+
+Manual compilation (it will be automatically included in the CMake build
+if building tools is requested during CMake configuration):
+
+```bash
+g++ -I <path/to/lammps/src> -o reformat-json reformat-json.cpp
+```
+
 -------
 
 updated by Axel Kohlmeyer, 2025-05-23
diff --git a/tools/json/reformat-json.cpp b/tools/json/reformat-json.cpp
new file mode 100644
index 0000000000..54897233b4
--- /dev/null
+++ b/tools/json/reformat-json.cpp
@@ -0,0 +1,47 @@
+
+#include "json.h"
+
+#include <cerrno>
+#include <cstdio>
+#include <string>
+
+using json = LAMMPS_NS::json;
+
+int main(int argc, char **argv)
+{
+  if (argc < 3) {
+    printf("Usage: %s <indent-width> <json-file-1> [<json-file-2> ...]\n", argv[0]);
+    return 1;
+  }
+
+  int indent = std::stoi(argv[1]);
+
+  // loop over files
+
+  for (int i=2; i < argc; ++i) {
+    std::string file = argv[i];
+    std::string backup = file + ".bak";
+
+    FILE *fp = fopen(file.c_str(), "r");
+    if (!fp) {
+      printf("Cannot open file %s for reading: %s\n", file.c_str(), strerror(errno));
+      return 2;
+    }
+
+    auto jsondata = json::parse(fp, nullptr, true, true);
+    fclose(fp);
+
+    rename(file.c_str(), backup.c_str());
+
+    fp = fopen(file.c_str(), "w");
+    if (!fp) {
+      printf("Cannot open file %s for writing: %s\n", file.c_str(), strerror(errno));
+      return 3;
+    }
+    std::string data = jsondata.dump(indent);
+    data += '\n';
+    fputs(data.c_str(), fp);
+    fclose(fp);
+  }
+  return 0;
+}