diff --git a/src/applib/command_executor_areca.h b/src/applib/command_executor_areca.h
index a481625..cc53dd8 100644
--- a/src/applib/command_executor_areca.h
+++ b/src/applib/command_executor_areca.h
@@ -76,7 +76,7 @@ ArecaCliExecutorGeneric<ExecutorPolicy>::ArecaCliExecutorGeneric()
 template<class ExecutorPolicy>
 std::string ArecaCliExecutorGeneric<ExecutorPolicy>::translate_exit_status([[maybe_unused]] int status)
 {
-	return std::string();
+	return {};
 }
 
 
diff --git a/src/applib/examples/example_smartctl_executor.cpp b/src/applib/examples/example_smartctl_executor.cpp
index 6314d4d..db8292b 100644
--- a/src/applib/examples/example_smartctl_executor.cpp
+++ b/src/applib/examples/example_smartctl_executor.cpp
@@ -38,7 +38,7 @@ int main(int argc, char** argv)
 
 		ex.execute();
 
-		std::string out_str = ex.get_stdout_str();
+		const std::string out_str = ex.get_stdout_str();
 	// 	std::cout << "OUT:\n" << out_str << "\n\n";
 		std::cerr << "OUT SIZE: " << out_str.size() << "\n";
 
diff --git a/src/applib/smartctl_ata_json_parser.cpp b/src/applib/smartctl_ata_json_parser.cpp
index 81ca54d..49d14a3 100644
--- a/src/applib/smartctl_ata_json_parser.cpp
+++ b/src/applib/smartctl_ata_json_parser.cpp
@@ -9,6 +9,8 @@ Copyright:
 /// \weakgroup applib
 /// @{
 
+#include <format>
+
 #include "smartctl_ata_json_parser.h"
 #include "json/json.hpp"
 #include "hz/debug.h"
@@ -93,7 +95,7 @@ T get_node_data(const nlohmann::json& root, const std::string& path)
 		const std::string& comp_name = components[comp_index];
 
 		if (!curr->is_object()) {  // we can't have non-object values in the middle of a path
-			throw std::runtime_error("Cannot get node data \""s + path + "\", component \"" + comp_name + "\" is not an object.");
+			throw std::runtime_error(std::format("Cannot get node data \"{}\", component \"{}\" is not an object.", path, comp_name));
 		}
 		if (auto iter = curr->find(comp_name); iter != curr->end()) {  // path component exists
 			const auto& jval = iter.value();
@@ -109,7 +111,7 @@ T get_node_data(const nlohmann::json& root, const std::string& path)
 			curr = &jval;
 
 		} else {  // path component doesn't exist
-			throw std::runtime_error("Cannot get node data \""s + path + "\", component \"" + comp_name + "\" does not exist.");
+			throw std::runtime_error(std::format("Cannot get node data \"{}\", component \"{}\" does not exist.", path, comp_name));
 		}
 	}
 
@@ -197,6 +199,8 @@ hz::ExpectedVoid<SmartctlParserError> SmartctlAtaJsonParser::parse_full(const st
 		debug_out_warn("app", DBG_FUNC_MSG << "Error parsing smartctl output as JSON: " << e.what() << "\n");
 		return hz::Unexpected(SmartctlParserError::SyntaxError, std::string("Invalid JSON data: ") + e.what());
 	}
+
+	return {};
 }
 
 
diff --git a/src/gsc_executor_error_dialog.cpp b/src/gsc_executor_error_dialog.cpp
index ae2c48e..106cf05 100644
--- a/src/gsc_executor_error_dialog.cpp
+++ b/src/gsc_executor_error_dialog.cpp
@@ -56,7 +56,7 @@ namespace {
 		dialog.set_default_response(Gtk::RESPONSE_OK);
 
 
-		int response = dialog.run();  // blocks until the dialog is closed
+		const int response = dialog.run();  // blocks until the dialog is closed
 
 		return response;
 	}
@@ -70,7 +70,7 @@ namespace {
 void gsc_executor_error_dialog_show(const std::string& message, const std::string& sec_message,
 		Gtk::Window* parent, bool sec_msg_markup, bool show_output_button)
 {
-	int response = show_executor_dialog(Gtk::MESSAGE_ERROR, message, sec_message,
+	const int response = show_executor_dialog(Gtk::MESSAGE_ERROR, message, sec_message,
 			parent, sec_msg_markup, show_output_button);
 
 	if (response == Gtk::RESPONSE_HELP) {
@@ -87,7 +87,7 @@ void gsc_no_info_dialog_show(const std::string& message, const std::string& sec_
 		Gtk::Window* parent, bool sec_msg_markup, const std::string& output,
 		const std::string& output_window_title, const std::string& default_save_filename)
 {
-	int response = show_executor_dialog(Gtk::MESSAGE_WARNING, message, sec_message,
+	const int response = show_executor_dialog(Gtk::MESSAGE_WARNING, message, sec_message,
 			parent, sec_msg_markup, !output.empty());
 
 	if (response == Gtk::RESPONSE_HELP) {
diff --git a/src/hz/bad_cast_exception.h b/src/hz/bad_cast_exception.h
index b8328f0..b5a9f70 100644
--- a/src/hz/bad_cast_exception.h
+++ b/src/hz/bad_cast_exception.h
@@ -47,7 +47,7 @@ class bad_cast_except : public std::exception {  // from <exception>
 		{
 			// Note: we do quite a lot of construction here, but since it's not
 			// an out-of-memory exception, what the heck.
-			std::string who = (self_name_.empty() ? "[unknown]" : self_name_);
+			const std::string who = (self_name_.empty() ? "[unknown]" : self_name_);
 
 			std::string from = (src_type_ == typeid(void) ? "[unknown]" : hz::type_name_demangle(src_type_.name()));
 			if (from.empty())
diff --git a/src/hz/format_unit.h b/src/hz/format_unit.h
index e57deb0..73c83c0 100644
--- a/src/hz/format_unit.h
+++ b/src/hz/format_unit.h
@@ -163,13 +163,13 @@ inline std::string format_time_length(std::chrono::seconds secs)
 
 	if (secs >= 100h) {
 		day_unit days = std::chrono::round<day_unit>(secs);
-		std::chrono::seconds sec_diff = secs - days;  // difference between days and actual time (may be positive or negative)
+		const std::chrono::seconds sec_diff = secs - days;  // difference between days and actual time (may be positive or negative)
 
 		if (days.count() < 10) {  // if less than 10 days, display hours too
 
 			// if there's more than half an hour missing from complete day, add a day.
 			// then add half an hour and convert to hours.
-			int64_t hours = ((sec_diff.count() < (-hour_size / 2) ? sec_diff.count() + day_size : sec_diff.count()) + hour_size / 2) / hour_size;
+			const int64_t hours = ((sec_diff.count() < (-hour_size / 2) ? sec_diff.count() + day_size : sec_diff.count()) + hour_size / 2) / hour_size;
 		    if (hours > 0 && sec_diff.count() < (-hour_size / 2))
 		       days--;
 
@@ -185,10 +185,10 @@ inline std::string format_time_length(std::chrono::seconds secs)
 
 	if (secs >= 100min) {
 		auto hours = std::chrono::round<std::chrono::hours>(secs);
-		std::chrono::seconds sec_diff = secs - hours;
+		const std::chrono::seconds sec_diff = secs - hours;
 
 		if (hours.count() < 10) {  // if less than 10 hours, display minutes too
-			int64_t minutes = ((sec_diff.count() < (-min_size / 2) ? sec_diff.count() + hour_size : sec_diff.count()) + min_size / 2) / min_size;
+			const int64_t minutes = ((sec_diff.count() < (-min_size / 2) ? sec_diff.count() + hour_size : sec_diff.count()) + min_size / 2) / min_size;
 			if (minutes > 0 && sec_diff.count() < (-min_size / 2))
 				hours--;
 
diff --git a/src/hz/fs.h b/src/hz/fs.h
index cc7566c..3f6e767 100644
--- a/src/hz/fs.h
+++ b/src/hz/fs.h
@@ -210,7 +210,7 @@ inline std::error_code fs_file_get_contents_noalloc(const fs::path& file, unsign
 		}
 
 		// automatically allocate the buffer if buf_size is -1.
-		bool auto_alloc = (buf_size == static_cast<std::uintmax_t>(-1));
+		const bool auto_alloc = (buf_size == static_cast<std::uintmax_t>(-1));
 		if (!auto_alloc && buf_size < size) {
 			ec = std::make_error_code(std::errc::no_buffer_space);
 			break;  // goto cleanup
@@ -225,7 +225,7 @@ inline std::error_code fs_file_get_contents_noalloc(const fs::path& file, unsign
 		// We don't need large file support here because we read into memory,
 		// which is limited at 31 bits anyway (on 32-bit systems).
 		// I really hope this is not a byte-by-byte operation
-		std::size_t read_bytes = std::fread(buf, 1, static_cast<std::size_t>(size), f);
+		const std::size_t read_bytes = std::fread(buf, 1, static_cast<std::size_t>(size), f);
 		if (size != static_cast<std::uintmax_t>(read_bytes)) {
 			// Unexpected number of bytes read. Not sure if this is reflected in errno or not.
 			ec = std::error_code(errno, std::system_category());
@@ -274,7 +274,7 @@ inline std::error_code fs_file_get_contents(const fs::path& file, std::string& p
 {
 	std::uintmax_t size = 0;
 	unsigned char* buf = nullptr;
-	std::error_code ec = fs_file_get_contents(file, buf, size, max_size);
+	const std::error_code ec = fs_file_get_contents(file, buf, size, max_size);
 	if (ec)
 		return ec;
 
@@ -497,13 +497,13 @@ inline bool fs_path_is_writable(const fs::path& path, std::error_code& ec)
 	}
 
 	std::error_code ignored_ec;  // ignore this error
-	bool is_directory = fs::is_directory(path, ignored_ec);
-	bool path_exists = fs::exists(path, ec);
+	const bool is_directory = fs::is_directory(path, ignored_ec);
+	const bool path_exists = fs::exists(path, ec);
 	if (ec) {
 		return false;
 	}
 
-	fs::path dirname = (is_directory ? path : path.parent_path());
+	const fs::path dirname = (is_directory ? path : path.parent_path());
 
 #ifdef _WIN32  // win32 doesn't get access() (it just doesn't work with writing)
 
diff --git a/src/libdebug/dchannel.cpp b/src/libdebug/dchannel.cpp
index 8e543ef..d7da740 100644
--- a/src/libdebug/dchannel.cpp
+++ b/src/libdebug/dchannel.cpp
@@ -33,11 +33,11 @@ std::string debug_format_message(debug_level::flag level, const std::string& dom
 		}
 
 		if (format_flags.test(debug_format::level)) {  // print level name
-			bool use_color = format_flags.test(debug_format::color);
+			const bool use_color = format_flags.test(debug_format::color);
 			if (use_color)
 				ret += debug_level::get_color_start(level);
 
-			std::string level_name = std::string("<") + debug_level::get_name(level) + ">";
+			const std::string level_name = std::string("<") + debug_level::get_name(level) + ">";
 			ret += level_name + std::string(8 - level_name.size(), ' ');
 
 			if (use_color)
@@ -52,7 +52,7 @@ std::string debug_format_message(debug_level::flag level, const std::string& dom
 
 
 	if (format_flags.test(debug_format::indent)) {
-		std::string spaces(static_cast<std::size_t>(indent_level * 4), ' ');  // indentation spaces
+		const std::string spaces(static_cast<std::size_t>(indent_level * 4), ' ');  // indentation spaces
 
 		// replace all newlines with \n(indent-spaces) except for the last one.
 		std::string::size_type oldpos = 0, pos = 0;
diff --git a/src/libdebug/dcmdarg.cpp b/src/libdebug/dcmdarg.cpp
index c18e773..f55dceb 100644
--- a/src/libdebug/dcmdarg.cpp
+++ b/src/libdebug/dcmdarg.cpp
@@ -91,7 +91,7 @@ static gboolean debug_internal_parse_levels([[maybe_unused]] const gchar* option
 	if (!value)
 		return FALSE;
 	auto* args = static_cast<debug_internal::DebugCmdArgs*>(data);
-	std::string levels = value;
+	const std::string levels = value;
 	hz::string_split(levels, ',', args->debug_levels, true);
 	// will filter out invalid ones later
 	return TRUE;
@@ -143,7 +143,7 @@ static gboolean debug_internal_post_parse_func([[maybe_unused]] GOptionContext*
 		if (args->verbosity_level > 4) args->levels_enabled.set(debug_level::dump);
 	}
 
-	bool color_enabled = static_cast<bool>(args->debug_colorize);
+	const bool color_enabled = static_cast<bool>(args->debug_colorize);
 
 
 	debug_internal::DebugState::DomainMap& domain_map = debug_internal::get_debug_state_ref().get_domain_map_ref();
diff --git a/src/libdebug/dout.cpp b/src/libdebug/dout.cpp
index f1ddef7..d89c81d 100644
--- a/src/libdebug/dout.cpp
+++ b/src/libdebug/dout.cpp
@@ -29,13 +29,13 @@ std::ostream& debug_out(debug_level::flag level, const std::string& domain)
 	auto level_map = dm.find(domain);
 	if (level_map == dm.end()) {  // no such domain
 		// this is an internal error
-		std::string msg = "debug_out(): Debug state doesn't contain the requested domain: \"" + domain + "\".";
+		const std::string msg = "debug_out(): Debug state doesn't contain the requested domain: \"" + domain + "\".";
 		throw debug_internal_error(msg.c_str());
 	}
 
 	auto os = level_map->second.find(level);
 	if (level_map == dm.end()) {
-		std::string msg = std::string("debug_out(): Debug state doesn't contain the requested level ") +
+		const std::string msg = std::string("debug_out(): Debug state doesn't contain the requested level ") +
 				debug_level::get_name(level) + " in domain: \"" + domain + "\".";
 
 		// this is an internal error
@@ -110,7 +110,7 @@ namespace debug_internal {
 // increase indentation level for all debug levels
 void debug_indent_inc(int by)
 {
-	int curr = debug_internal::get_debug_state_ref().get_indent_level();
+	const int curr = debug_internal::get_debug_state_ref().get_indent_level();
 	debug_internal::get_debug_state_ref().set_indent_level(curr + by);
 }
 
diff --git a/src/libdebug/dstate.cpp b/src/libdebug/dstate.cpp
index 3e76525..d0a3f7e 100644
--- a/src/libdebug/dstate.cpp
+++ b/src/libdebug/dstate.cpp
@@ -44,7 +44,7 @@ namespace debug_internal {
 		format_flags.set(debug_format::color);
 #endif
 
-		std::map<debug_level::flag, bool> levels = {
+		const std::map<debug_level::flag, bool> levels = {
 				{debug_level::dump, levels_enabled.test(debug_level::dump) },
 				{debug_level::info, levels_enabled.test(debug_level::info) },
 				{debug_level::warn, levels_enabled.test(debug_level::warn) },
@@ -102,7 +102,7 @@ bool debug_register_domain(const std::string& domain)
 			+ "\"): Domain \"default\" doesn't exist.").c_str());
 	}
 
-	DebugState::LevelMap& def_level_map = def_iter->second;
+	const DebugState::LevelMap& def_level_map = def_iter->second;
 
 	dm[domain] = DebugState::LevelMap();
 	DebugState::LevelMap& level_map = dm.find(domain)->second;
diff --git a/src/libdebug/dstate.h b/src/libdebug/dstate.h
index bb06138..fb84235 100644
--- a/src/libdebug/dstate.h
+++ b/src/libdebug/dstate.h
@@ -85,7 +85,7 @@ namespace debug_internal {
 			{
 				if (inside_begin_.empty())
 					throw debug_usage_error("DebugState::pop_inside_begin(): Begin / End stack underflow! Mismatched begin()/end()?");
-				bool val = inside_begin_.top();
+				const bool val = inside_begin_.top();
 				inside_begin_.pop();
 				return val;
 			}
diff --git a/src/libdebug/examples/example_libdebug.cpp b/src/libdebug/examples/example_libdebug.cpp
index a25391f..ca8b118 100644
--- a/src/libdebug/examples/example_libdebug.cpp
+++ b/src/libdebug/examples/example_libdebug.cpp
@@ -78,9 +78,9 @@ int main_impl()
 	));
 
 
-	std::string something = "some thing";
+	const std::string something = "some thing";
 	const char* obj = "obj";
-	int op = 5;
+	const int op = 5;
 
 
 	debug_out_dump("dom", "Dumping something: " << something << std::endl);
diff --git a/src/rconfig/examples/example_rconfig.cpp b/src/rconfig/examples/example_rconfig.cpp
index 9b5ab2b..930562b 100644
--- a/src/rconfig/examples/example_rconfig.cpp
+++ b/src/rconfig/examples/example_rconfig.cpp
@@ -48,7 +48,7 @@ int main()
 
 		rconfig::set_data("app/int_var", 11);  // override default.
 
-		int int_var = rconfig::get_data<int>("app/int_value");
+		const int int_var = rconfig::get_data<int>("app/int_value");
 		std::cerr << "app/int_value: " << int_var << "\n";
 
 		std::cerr << "app/some_string2: " << rconfig::get_data<std::string>("app/some_string2") << "\n";
diff --git a/src/test_all/test_all.cpp b/src/test_all/test_all.cpp
index 21a63b8..6676911 100644
--- a/src/test_all/test_all.cpp
+++ b/src/test_all/test_all.cpp
@@ -29,7 +29,7 @@ int main(int argc, char* argv[])
 	debug_register_domain("hz");
 	debug_register_domain("rconfig");
 
-	int result = Catch::Session().run( argc, argv );
+	const int result = Catch::Session().run( argc, argv );
 	return result;
 }