diff --git a/src/gui/add_csv_window.cpp b/src/gui/add_csv_window.cpp
index f63ca508..9fca299e 100644
--- a/src/gui/add_csv_window.cpp
+++ b/src/gui/add_csv_window.cpp
@@ -167,7 +167,7 @@ void AddCSVWindow::onOk(wxCommandEvent&) {
   /// Perform the import
   wxBusyCursor wait;
   // Read the file
-  auto file = std::ifstream(file_path->GetValue().ToStdString());
+  auto& file = std::ifstream(file_path->GetValue().ToStdString());
   if (file.fail()) {
     queue_message(MESSAGE_ERROR, _ERROR_("add card csv file not found"));
     EndModal(wxID_ABORT);
diff --git a/src/gui/add_json_window.cpp b/src/gui/add_json_window.cpp
index c17df358..dba748a8 100644
--- a/src/gui/add_json_window.cpp
+++ b/src/gui/add_json_window.cpp
@@ -139,14 +139,14 @@ void AddJSONWindow::onBrowseFiles(wxCommandEvent&) {
     queue_message(MESSAGE_ERROR, _ERROR_("add card json empty array"));
     return false;
   }
-  auto& card = card_array[0];
-  if (!card.is_object()) {
+  const auto& first_card = card_array[0];
+  if (!first_card.is_object()) {
     queue_message(MESSAGE_ERROR, _ERROR_("add card json path not valid"));
     return false;
   }
   // Get headers
   for (int i = 0; i < count; ++i) {
-    auto& card = card_array[i].as_object();
+    const auto& card = card_array[i].as_object();
     for (auto it = card.begin(); it != card.end(); ++it) {
       boost::json::string_view jview = it->key();
       std::string_view stdview = std::string_view(jview.data(), jview.size());
@@ -162,7 +162,7 @@ void AddJSONWindow::onBrowseFiles(wxCommandEvent&) {
     std::vector<ScriptValueP> row;
     auto& card = card_array[i].as_object();
     for (int h = 0; h < headers_out.size(); ++h) {
-      auto& value = card[headers_out[h].ToStdString()];
+      const auto& value = card[headers_out[h].ToStdString()];
       row.push_back(json_to_mse(value, set.get()));
     }
     table_out.push_back(row);
@@ -174,7 +174,7 @@ void AddJSONWindow::onOk(wxCommandEvent&) {
   /// Perform the import
   wxBusyCursor wait;
   // Read the file
-  auto file = std::ifstream(file_path->GetValue().ToStdString());
+  auto& file = std::ifstream(file_path->GetValue().ToStdString());
   if (file.fail()) {
     queue_message(MESSAGE_ERROR, _ERROR_("add card json file not found"));
     EndModal(wxID_ABORT);
diff --git a/src/script/functions/json.hpp b/src/script/functions/json.hpp
index 52b07ed1..3d1b279d 100644
--- a/src/script/functions/json.hpp
+++ b/src/script/functions/json.hpp
@@ -25,7 +25,7 @@
 
 // ----------------------------------------------------------------------------- : JSON to String
 
-inline static void pretty_print(std::ostream& os, boost::json::value const& jv, std::string* indent = nullptr)
+inline static void pretty_print(std::ostream& os, const boost::json::value& jv, std::string* indent = nullptr)
 {
   std::string indent_;
   if(! indent)
@@ -106,21 +106,21 @@ inline static void pretty_print(std::ostream& os, boost::json::value const& jv,
     os << "\n";
 }
 
-inline static String json_pretty_print(boost::json::value const& jv, std::string* indent = nullptr) {
+inline static String json_pretty_print(const boost::json::value& jv, std::string* indent = nullptr) {
   std::ostringstream stream;
   pretty_print(stream, jv, indent);
   String string = wxString(stream.str().c_str());
   return string;
 }
 
-inline static String json_ugly_print(boost::json::value const& jv) {
+inline static String json_ugly_print(const boost::json::value& jv) {
   String string = wxString(boost::json::serialize(jv).c_str());
   return string;
 }
 
 // ----------------------------------------------------------------------------- : JSON to MSE
 
-inline static ScriptValueP json_to_mse(boost::json::value& jv, Set* set);
+inline static ScriptValueP json_to_mse(const boost::json::value& jv, Set* set);
 
 template <typename T>
 static void read(T& out, boost::json::object& jv, const char value_name[]) {
@@ -301,7 +301,7 @@ inline static SetP json_to_mse_set(boost::json::object& jv) {
   return set;
 }
 
-inline static ScriptValueP json_to_mse(boost::json::value& jv, Set* set) {
+inline static ScriptValueP json_to_mse(const boost::json::value& jv, Set* set) {
   if (jv == nullptr) return script_nil;
   else if (jv.is_null()) return script_nil;
   else if (jv.is_bool()) return to_script(jv.get_bool());
@@ -358,7 +358,7 @@ inline static ScriptValueP json_to_mse(boost::json::value& jv, Set* set) {
     return script_nil;
   }
 }
-inline static ScriptValueP json_to_mse(String& string, Set* set) {
+inline static ScriptValueP json_to_mse(const String& string, Set* set) {
   try {
     boost::system::error_code ec;
     boost::json::parse_options options;
@@ -372,7 +372,7 @@ inline static ScriptValueP json_to_mse(String& string, Set* set) {
     return script_nil;
   }
 }
-inline static ScriptValueP json_to_mse(ScriptValueP& sv, Set* set) {
+inline static ScriptValueP json_to_mse(const ScriptValueP& sv, Set* set) {
   try {
     String string = sv->toString();
     return json_to_mse(string, set);
@@ -386,7 +386,7 @@ inline static ScriptValueP json_to_mse(ScriptValueP& sv, Set* set) {
 // ----------------------------------------------------------------------------- : MSE to JSON
 
 template <typename T>
-static void write(boost::json::object& out, const String& name, T& value) {
+static void write(boost::json::object& out, const String& name, const T& value) {
   wxStringOutputStream stream;
   Writer writer(stream);
   writer.indentation = -1000;