diff --git a/CMakeLists.txt b/CMakeLists.txt
index ec0769e..d96662a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -67,10 +67,6 @@ elseif (EMSCRIPTEN)
     )
 
 else()  # NOT (ANDROID OR EMSCRIPTEN)
-  if (NOT NINTENDO_SWITCH)
-    option(ENABLE_DEBUGGER "Enable built-in debugger" ON)
-  endif()
-
   add_executable(system3)
   target_link_libraries(system3 PRIVATE ymfm)
 
@@ -117,6 +113,13 @@ else()  # NOT (ANDROID OR EMSCRIPTEN)
     pkg_check_modules(SDL2 REQUIRED IMPORTED_TARGET sdl2)
     pkg_check_modules(SDL2TTF REQUIRED IMPORTED_TARGET SDL2_ttf)
     target_link_libraries(system3 PRIVATE PkgConfig::SDL2 PkgConfig::SDL2TTF)
+
+    find_package(nlohmann_json 3.2.0)
+    if (nlohmann_json_FOUND)
+      set(ENABLE_DEBUGGER ON)
+      target_link_libraries(system3 PRIVATE nlohmann_json::nlohmann_json)
+    endif()
+
     pkg_check_modules(RTMIDI IMPORTED_TARGET rtmidi)
     if (RTMIDI_FOUND)
       target_compile_definitions(system3 PRIVATE USE_MIDI)
@@ -186,6 +189,7 @@ if (ENABLE_DEBUGGER)
     src/debugger/debug_info.cpp
     src/debugger/debugger.cpp
     src/debugger/cli_frontend.cpp
+    src/debugger/dap_frontend.cpp
   )
 endif()
 
diff --git a/src/common.h b/src/common.h
index b1ee275..96324fe 100644
--- a/src/common.h
+++ b/src/common.h
@@ -55,6 +55,11 @@ inline void strcpy_s(char* dst, size_t n, const char* src)
 #define strcasecmp _stricmp
 #endif
 
+extern uint32_t sdl_custom_event_type;
+enum CustomEvent {
+	DEBUGGER_COMMAND,
+};
+
 // resource.cpp
 SDL_RWops* open_resource(const char* name, const char* type);
 SDL_RWops* open_file(const char* name);
diff --git a/src/config.cpp b/src/config.cpp
index 9c66c71..cccdaa1 100644
--- a/src/config.cpp
+++ b/src/config.cpp
@@ -132,6 +132,8 @@ Config::Config(int argc, char *argv[])
 	for (int i = 1; i < argc; i++) {
 		if (strcmp(argv[i], "-gamedir") == 0)
 			++i;
+		else if (strcmp(argv[i], "-version") == 0)
+			print_version = true;
 		else if (strcmp(argv[i], "-noantialias") == 0)
 			no_antialias = true;
 		else if (strcmp(argv[i], "-savedir") == 0)
diff --git a/src/config.h b/src/config.h
index 7a0c617..315bdfe 100644
--- a/src/config.h
+++ b/src/config.h
@@ -41,6 +41,7 @@ struct Config {
 	std::string playlist;
 	std::string title;
 	int midi_device = -1;
+	bool print_version = false;
 	bool use_fm = false;
 	bool no_antialias = false;
 	bool scanline = false;
diff --git a/src/debugger/cli_frontend.cpp b/src/debugger/cli_frontend.cpp
index 4ee799d..bb0c2de 100644
--- a/src/debugger/cli_frontend.cpp
+++ b/src/debugger/cli_frontend.cpp
@@ -42,6 +42,8 @@ public:
 
 	~CliFrontend() override = default;
 
+	void init() override {}
+
 	void repl(int bp_no) override {
 		if (backend->get_state() == State::STOPPED_BREAKPOINT && bp_no)
 			printf("Breakpoint %d\n", bp_no);
@@ -67,6 +69,9 @@ public:
 			}
 		}
 	}
+
+	void on_command(void* data) override {}
+
 	void on_sleep() override  {
 		if (backend->get_state() == State::STOPPED_INTERRUPT)
 			backend->repl(0);
@@ -75,7 +80,8 @@ public:
 	void on_palette_change() override {
 	}
 
-	void console_output(int lv, const char *output) override {
+	bool console_output(const char* format, va_list ap) override {
+		return false;
 	}
 
 private:
diff --git a/src/debugger/dap_frontend.cpp b/src/debugger/dap_frontend.cpp
new file mode 100644
index 0000000..cf8f46e
--- /dev/null
+++ b/src/debugger/dap_frontend.cpp
@@ -0,0 +1,512 @@
+#define JSON_USE_IMPLICIT_CONVERSIONS 0
+
+#include "debugger/frontend.h"
+#include <algorithm>
+#include <queue>
+#include <SDL.h>
+#include "nlohmann/json.hpp"
+#include "common.h"
+#include "encoding.h"
+#include "nact.h"
+#include "debugger/debugger.h"
+using Json = nlohmann::json;
+
+namespace debugger {
+
+namespace {
+
+enum VariablesReference {
+	VREF_GLOBALS = 1,
+	VREF_STRINGS,
+};
+
+void post_debugger_command(void *data) {
+	SDL_Event event = {};
+	event.user.type = sdl_custom_event_type;
+	event.user.code = DEBUGGER_COMMAND;
+	event.user.data1 = data;
+	SDL_PushEvent(&event);
+}
+
+int read_command_thread(void*) {
+	int content_length = -1;
+	char header[512];
+	while (fgets(header, sizeof(header), stdin)) {
+		if (sscanf(header, "Content-Length: %d", &content_length) == 1) {
+			continue;
+		} else if ((header[0] == '\r' && header[1] == '\n') || header[0] == '\n') {
+			if (content_length < 0) {
+				fprintf(stderr, "Debug Adapter Protocol error: no Content-Length header\n");
+				continue;
+			}
+			char* buf = (char*)malloc(content_length + 1);
+			fread(buf, content_length, 1, stdin);
+			buf[content_length] = '\0';
+			post_debugger_command(buf);
+			content_length = -1;
+		} else {
+			fprintf(stderr, "Unknown Debug Adapter Protocol header: %s", header);
+		}
+	}
+	post_debugger_command(NULL);  // end of messages
+	return 0;
+}
+
+} // namespace
+
+class DapFrontend : public Frontend {
+public:
+	DapFrontend(Debugger* backend, const DebugInfo& symbols) : Frontend(backend, symbols) {
+		SDL_CreateThread(read_command_thread, "Debugger", NULL);
+	}
+
+	void init() override {
+		while (!initialized && !g_nact->is_terminating()) {
+			g_nact->process_next_event();
+			while (!queue.empty()) {
+				char* msg = queue.front();
+				queue.pop();
+				if (!msg)
+					return;
+				handle_message(msg);
+			}
+		}
+	}
+
+	void repl(int bp_no) override {
+		emit_stopped_event();
+		backend->set_state(State::RUNNING);
+
+		bool continue_repl = true;
+		while (continue_repl && !g_nact->is_terminating()) {
+			g_nact->process_next_event();
+			while (!queue.empty()) {
+				char* msg = queue.front();
+				queue.pop();
+				if (!msg)
+					return;
+				continue_repl = handle_message(msg);
+			}
+		}
+	}
+
+	void on_command(void* data) override {
+		queue.push(static_cast<char*>(data));
+	}
+
+	void on_sleep() override  {
+		while (!queue.empty()) {
+			char* msg = queue.front();
+			queue.pop();
+			if (!msg)
+				return;
+			handle_message(msg);
+		}
+		if (backend->get_state() == State::STOPPED_INTERRUPT || backend->get_state() == State::STOPPED_EXCEPTION)
+			backend->repl(0);
+	}
+
+	void on_palette_change() override {
+	}
+
+	bool console_output(const char* format, va_list ap) override {
+		return true;
+	}
+
+private:
+	Json create_source(const char *name) {
+		Json source;
+		source["name"] = name;
+		if (!src_dir.empty())
+			source["path"] = src_dir + "/" + name;
+		source["sourceReference"] = 0;
+		return source;
+	}
+
+	std::string format_string_value(const char* str) {
+		char *utf = g_nact->encoding->toUtf8(str);
+		std::string value = "\"";
+		value += utf;
+		value += "\"";
+		free(utf);
+		return value;
+	}
+
+	void send_json(Json& json) {
+		json["seq"] = ++seq_;
+		std::string str = json.dump();
+		printf("Content-Length: %zu\r\n\r\n%s", str.size(), str.c_str());
+		fflush(stdout);
+	}
+
+	void emit_initialized_event() {
+		Json json = {
+			{"type", "event"},
+			{"event", "initialized"},
+		};
+		send_json(json);
+	}
+
+	void emit_stopped_event() {
+		std::string reason;
+		switch (backend->get_state()) {
+		case State::STOPPED_ENTRY: reason = "entry"; break;
+		case State::STOPPED_STEP: reason = "step"; break;
+		case State::STOPPED_NEXT: reason = "step"; break;
+		case State::STOPPED_BREAKPOINT: reason = "breakpoint"; break;
+		case State::STOPPED_INTERRUPT: reason = "pause"; break;
+		case State::STOPPED_EXCEPTION: reason = "exception"; break;
+		default: reason = "unknown"; break;
+		}
+		Json json = {
+			{"type", "event"},
+			{"event", "stopped"},
+			{"body", {
+				{"reason", reason},
+				{"allThreadsStopped", true},
+			}}
+		};
+		send_json(json);
+	}
+
+	bool handle_message(char* msg) {
+		Json json = Json::parse(msg);
+		auto type = json["type"].get<std::string>();
+		bool continue_repl = true;
+		if (type == "request")
+			continue_repl = handle_request(json);
+		free(msg);
+		return continue_repl;
+	}
+
+	bool handle_request(Json& request) {
+		Json resp;
+		resp["type"] = "response";
+		resp["request_seq"] = request["seq"];
+		resp["command"] = request["command"];
+		auto command = request["command"].get<std::string>();
+		Json& args = request["arguments"];
+
+		bool continue_repl = true;
+		if (command == "initialize") {
+			cmd_initialize(args, resp);
+		} else if (command == "disconnect") {
+			cmd_disconnect(args, resp);
+			continue_repl = false;
+		} else if (command == "launch") {
+			cmd_launch(args, resp);
+		} else if (command == "configurationDone") {
+			cmd_configurationDone(args, resp);
+		} else if (command == "threads") {
+			cmd_threads(args, resp);
+		} else if (command == "scopes") {
+			cmd_scopes(args, resp);
+		} else if (command == "variables") {
+			cmd_variables(args, resp);
+		} else if (command == "setVariable") {
+			cmd_setVariable(args, resp);
+		} else if (command == "stackTrace") {
+			cmd_stackTrace(args, resp);
+		} else if (command == "evaluate") {
+			cmd_evaluate(args, resp);
+		} else if (command == "setBreakpoints") {
+			cmd_setBreakpoints(args, resp);
+		} else if (command == "continue") {
+			cmd_continue(args, resp);
+			continue_repl = false;
+		} else if (command == "pause") {
+			cmd_pause(args, resp);
+		} else if (command == "stepIn") {
+			cmd_stepIn(args, resp);
+			continue_repl = false;
+		} else if (command == "stepOut") {
+			cmd_stepOut(args, resp);
+			continue_repl = false;
+		} else if (command == "next") {
+			cmd_next(args, resp);
+			continue_repl = false;
+		} else {
+			fprintf(stderr, "Unknown command '%s'\n", command.c_str());
+			resp["success"] = false;
+			resp["message"] = "Unknown command " + command;
+		}
+		send_json(resp);
+		return continue_repl;
+	}
+
+	void cmd_initialize(Json& args, Json& resp) {
+		resp["success"] = true;
+		resp["body"] = {
+			{"supportsConfigurationDoneRequest", true},
+			{"supportsEvaluateForHovers", true},
+			{"supportsSetVariable", true},
+		};
+	}
+
+	void cmd_disconnect(Json& args, Json& resp) {
+		resp["success"] = true;
+		g_nact->quit(0);
+	}
+
+	void cmd_launch(Json& args, Json& resp) {
+		if (args["noDebug"].is_boolean() && args["noDebug"].get<bool>()) {
+			resp["success"] = true;
+			initialized = true;
+			return;
+		}
+
+		if (!symbols.loaded()) {
+			resp["success"] = false;
+			resp["message"] = "system3: Cannot load debug symbols";
+			return;
+		}
+
+		if (args["srcDir"].is_string())
+			src_dir = args["srcDir"].get<std::string>();
+		if (args["stopOnEntry"].is_boolean() && args["stopOnEntry"].get<bool>())
+			backend->set_state(State::STOPPED_ENTRY);
+		resp["success"] = true;
+
+		emit_initialized_event();
+	}
+
+	void cmd_configurationDone(Json& args, Json& resp) {
+		initialized = true;
+		resp["success"] = true;
+	}
+
+	void cmd_threads(Json& args, Json& resp) {
+		resp["success"] = true;
+		resp["body"] = {
+			{"threads", {
+				{{"id", 1}, {"name", "main thread"}},
+			}}
+		};
+	}
+
+	void cmd_scopes(Json& args, Json& resp) {
+		resp["success"] = true;
+		resp["body"] = {
+			{"scopes", {
+				{
+					{"name", "All Variables"},
+					{"variablesReference", VREF_GLOBALS},
+					{"namedVariables", symbols.num_variables()},
+					{"expensive", false}
+				},
+				{
+					{"name", "Strings"},
+					{"variablesReference", VREF_STRINGS},
+					{"indexedVariables", MAX_STRVAR},
+					{"expensive", false}
+				},
+			}}
+		};
+	}
+
+	void cmd_variables(Json& args, Json& resp) {
+		const Json& start_ = args["start"];
+		const Json& count_ = args["count"];
+		int start = start_.is_number() ? start_.get<int>() : 0;
+		int count = count_.is_number() ? count_.get<int>() : MAX_VAR;
+
+		int var_ref = args["variablesReference"].get<int>();
+		if (var_ref == VREF_GLOBALS) {
+			resp["success"] = true;
+			Json& variables = resp["body"]["variables"];
+			int end = std::min(start + count, static_cast<int>(symbols.num_variables()));
+			for (int i = start; i < end; i++) {
+				Json item = {
+					{"name", symbols.variable_name(i)},
+					{"value", std::to_string(g_nact->get_var(i))},
+					{"variablesReference", 0},
+				};
+				variables.push_back(std::move(item));
+			}
+		} else if (var_ref == VREF_STRINGS) {
+			resp["success"] = true;
+			Json& variables = resp["body"]["variables"];
+			int end = std::min(start + count, MAX_STRVAR);
+			for (int i = start; i < end; i++) {
+				char name[10];
+				snprintf(name, sizeof(name), "[%d]", i + 1);
+				Json item = {
+					{"name", name},
+					{"value", format_string_value(g_nact->get_string(i))},
+					{"variablesReference", 0},
+				};
+				variables.push_back(std::move(item));
+			}
+		} else {
+			resp["success"] = false;
+			resp["message"] = "Invalid variables reference";
+		}
+	}
+
+	void cmd_setVariable(Json& args, Json& resp) {
+		switch (args["variablesReference"].get<int>()) {
+		case VREF_GLOBALS:
+			{
+				int var = symbols.lookup_variable(args["name"].get<std::string>().c_str());
+				if (var < 0) {
+					resp["success"] = false;
+					resp["message"] = "Invalid variable name";
+					return;
+				}
+				int parsed_value;
+				if (sscanf(args["value"].get<std::string>().c_str(), "%i", &parsed_value) != 1) {
+					resp["success"] = false;
+					resp["message"] = "Syntax error";
+					return;
+				}
+				g_nact->set_var(var, parsed_value);
+				resp["success"] = true;
+				resp["body"] = {
+					{"value", std::to_string(g_nact->get_var(var))},
+				};
+			}
+			break;
+		case VREF_STRINGS:
+			{
+				int index;
+				if (sscanf(args["name"].get<std::string>().c_str(), "[%d]", &index) != 1 || index <= 0 || index > MAX_STRVAR) {
+					resp["success"] = false;
+					resp["message"] = "Invalid string index";
+					return;
+				}
+				index--;  // 1-based to 0-based
+
+				std::string value = args["value"].get<std::string>();
+				if (value.size() < 2 || value[0] != '"' || value.back() != '"') {
+					resp["success"] = false;
+					resp["message"] = "Syntax error";
+					return;
+				}
+				value = value.substr(1, value.size() - 2);
+
+				char* encoded = g_nact->encoding->fromUtf8(value.c_str());
+				g_nact->set_string(index, encoded);
+				free(encoded);
+
+				resp["success"] = true;
+				resp["body"] = {
+					{"value", format_string_value(g_nact->get_string(index))},
+				};
+			}
+			break;
+		default:
+			resp["success"] = false;
+			resp["message"] = "Invalid variables reference";
+			break;
+		}
+	}
+
+	void cmd_stackTrace(Json& args, Json& resp) {
+		resp["success"] = true;
+		Json& body = resp["body"];
+		Json& stackFrames = body["stackFrames"];
+		int i = 0;
+		for (const StackFrame &frame : backend->stack_trace()) {
+			Json& item = stackFrames[i++];
+			item["id"] = i;
+			item["name"] = frame.src;
+			item["source"] = create_source(frame.src);
+			item["line"] = frame.line;
+			item["column"] = 0;
+		}
+		body["totalFrames"] = i;
+	}
+
+	void cmd_evaluate(Json& args, Json& resp) {
+		int var = symbols.lookup_variable(args["expression"].get<std::string>().c_str());
+		if (var < 0) {
+			resp["success"] = false;
+			resp["message"] = "Invalid expression";
+			return;
+		}
+		resp["success"] = true;
+		resp["body"] = {
+			{"result", std::to_string(g_nact->get_var(var))},
+			{"variablesReference", 0},
+		};
+	}
+
+	void cmd_setBreakpoints(Json& args, Json& resp) {
+		const auto filename = args["source"]["name"].get<std::string>();
+		int page = symbols.src2page(filename.c_str());
+
+		backend->delete_breakpoints_in_page(page);
+
+		resp["success"] = true;
+		Json& body = resp["body"];
+		Json& out_bps = body["breakpoints"];
+
+		for (const Json& srcbp : args["breakpoints"]) {
+			Json& item = out_bps.emplace_back();
+
+			int line = srcbp["line"].get<int>();
+			int addr = symbols.line2addr(page, line);
+			if (page < 0) {
+				item["verified"] = false;
+				item["message"] = "no source file named " + filename;
+				continue;
+			}
+			if (addr < 0) {
+				item["verified"] = false;
+				item["message"] = "no line " + std::to_string(line) + " in file " + filename;
+				continue;
+			}
+			int bp_no = backend->set_breakpoint(page, addr, false);
+			if (bp_no < 0) {
+				char message[256];
+				snprintf(message, sizeof(message), "failed to set breakpoint at %d:0x%x", page, addr);
+				item["verified"] = false;
+				item["message"] = message;
+				continue;
+			}
+
+			line = symbols.addr2line(page, addr);
+			item["id"] = bp_no;
+			item["verified"] = true;
+			item["source"] = create_source(filename.c_str());
+			item["line"] = line;
+		}
+	}
+
+	void cmd_continue(Json& args, Json& resp) {
+		// TODO: sdl_raiseWindow();
+		resp["success"] = true;
+	}
+
+	void cmd_pause(Json& args, Json& resp) {
+		backend->set_state(State::STOPPED_INTERRUPT);
+		resp["success"] = true;
+	}
+
+	void cmd_stepIn(Json& args, Json& resp) {
+		backend->stepin();
+		resp["success"] = true;
+	}
+
+	void cmd_stepOut(Json& args, Json& resp) {
+		backend->stepout();
+		resp["success"] = true;
+	}
+
+	void cmd_next(Json& args, Json& resp) {
+		backend->next();
+		resp["success"] = true;
+	}
+
+	std::queue<char*> queue;
+	bool initialized = false;
+	int seq_ = 0;
+	std::string src_dir;
+};
+
+// static
+Frontend* Frontend::create_dap(Debugger* backend, const DebugInfo& symbols) {
+	return new DapFrontend(backend, symbols);
+}
+
+} // namespace debugger
diff --git a/src/debugger/debugger.cpp b/src/debugger/debugger.cpp
index 121cdfd..758af8c 100644
--- a/src/debugger/debugger.cpp
+++ b/src/debugger/debugger.cpp
@@ -65,7 +65,7 @@ int get_retaddr_if_funcall() {
 Debugger::Debugger(const char *symbols_path, DebuggerMode mode) {
 	symbols.load(symbols_path);
 	if (mode == DebuggerMode::DAP) {
-		// frontend = std::make_unique<DapFrontend>(this);
+		frontend = std::unique_ptr<Frontend>(Frontend::create_dap(this, symbols));
 	} else {
 		frontend = std::unique_ptr<Frontend>(Frontend::create_cli(this, symbols));
 	}
@@ -73,6 +73,10 @@ Debugger::Debugger(const char *symbols_path, DebuggerMode mode) {
 
 Debugger::~Debugger() = default;
 
+void Debugger::init() {
+	frontend->init();
+}
+
 void Debugger::repl(int bp_no) {
 	delete_breakpoint(INTERNAL_BREAKPOINT_NO);
 
@@ -114,10 +118,12 @@ uint8_t Debugger::handle_breakpoint(int page, int addr) {
 	return restore_op;
 }
 
-bool Debugger::console_vprintf(int lv, const char *format, va_list ap) {
-	return false;
+bool Debugger::console_vprintf(const char *format, va_list ap) {
+	return frontend->console_output(format, ap);
 }
+
 void Debugger::post_command(void *data) {
+	frontend->on_command(data);
 }
 
 int Debugger::set_breakpoint(int page, int addr, bool is_internal)
diff --git a/src/debugger/debugger.h b/src/debugger/debugger.h
index b2749f6..624a493 100644
--- a/src/debugger/debugger.h
+++ b/src/debugger/debugger.h
@@ -41,11 +41,12 @@ public:
 	void repl(int bp_no);
 
 	// API for VM
+	void init();
 	bool trapped() const { return state != State::RUNNING; }
 	void on_sleep();
 	void on_palette_change();
 	uint8_t handle_breakpoint(int page, int addr);
-	bool console_vprintf(int lv, const char *format, va_list ap);
+	bool console_vprintf(const char *format, va_list ap);
 	void post_command(void *data);
 
 	// API for frontend
diff --git a/src/debugger/frontend.h b/src/debugger/frontend.h
index f441349..f5efb16 100644
--- a/src/debugger/frontend.h
+++ b/src/debugger/frontend.h
@@ -1,6 +1,8 @@
 #ifndef _DEBUGGER_FRONTEND_H_
 #define _DEBUGGER_FRONTEND_H_
 
+#include <stdarg.h>
+
 namespace debugger {
 
 class Debugger;
@@ -9,13 +11,16 @@ class DebugInfo;
 class Frontend {
 public:
 	static Frontend* create_cli(Debugger* backend, const DebugInfo& symbols);
+	static Frontend* create_dap(Debugger* backend, const DebugInfo& symbols);
 
 	Frontend(Debugger* backend, const DebugInfo& symbols) : backend(backend), symbols(symbols) {}
 	virtual ~Frontend() = default;
+	virtual void init() = 0;
 	virtual void repl(int bp_no) = 0;
+	virtual void on_command(void* data) = 0;
 	virtual void on_sleep() = 0;
 	virtual void on_palette_change() = 0;
-	virtual void console_output(int lv, const char *output) = 0;
+	virtual bool console_output(const char* format, va_list ap) = 0;
 protected:
 	Debugger* backend;
 	const DebugInfo& symbols;
diff --git a/src/generic/nact_generic.cpp b/src/generic/nact_generic.cpp
index eb86efa..340c66a 100644
--- a/src/generic/nact_generic.cpp
+++ b/src/generic/nact_generic.cpp
@@ -1,5 +1,6 @@
 #include <stdio.h>
 #include "nact.h"
+#include "debugger/debugger.h"
 
 void NACT::text_dialog()
 {
@@ -15,6 +16,16 @@ void NACT::platform_finalize()
 
 void NACT::output_console(const char *format, ...)
 {
+#ifdef ENABLE_DEBUGGER
+	if (g_debugger) {
+		va_list ap;
+		va_start(ap, format);
+		bool handled = g_debugger->console_vprintf(format, ap);
+		va_end(ap);
+		if (handled)
+			return;
+	}
+#endif
 #if defined(_DEBUG_CONSOLE)
 	va_list ap;
 
diff --git a/src/sdlmain.cpp b/src/sdlmain.cpp
index 0e0a14b..e278be8 100644
--- a/src/sdlmain.cpp
+++ b/src/sdlmain.cpp
@@ -69,16 +69,23 @@ SDL_Window* create_window(const GameId& game_id)
 
 } // namespace
 
+uint32_t sdl_custom_event_type;
+
 int main(int argc, char *argv[])
 {
 #ifdef __SWITCH__
 	romfsInit();
 #endif
 	Config config(argc, argv);
+	if (config.print_version) {
+		puts(SYSTEM3_VERSION);
+		return 0;
+	}
 	GameId game_id(config);
 
 	g_window = create_window(game_id);
 	g_renderer = SDL_CreateRenderer(g_window, -1, 0);
+	sdl_custom_event_type = SDL_RegisterEvents(1);
 
 	// system3 初期化
 	g_nact.reset(NACT::create(config, game_id));
@@ -112,6 +119,7 @@ int main(int argc, char *argv[])
 #ifdef ENABLE_DEBUGGER
 	if (config.debugger_mode != DebuggerMode::DISABLED) {
 		g_debugger = std::make_unique<debugger::Debugger>("ADISK.DAT.symbols", config.debugger_mode);
+		g_debugger->init();
 	}
 #endif
 
diff --git a/src/sys/nact.cpp b/src/sys/nact.cpp
index 5542d09..3e9b9e9 100644
--- a/src/sys/nact.cpp
+++ b/src/sys/nact.cpp
@@ -6,6 +6,7 @@
 
 #include <stdarg.h>
 #include <stdlib.h>
+#include <string.h>
 #include "nact.h"
 #include "encoding.h"
 #include "ags.h"
@@ -843,6 +844,23 @@ void NACT::sys_sleep(int ms) {
 #endif
 }
 
+void NACT::set_string(int index, const char* value)
+{
+	const char *src = value;
+	char *dst = tvar[index];
+	int remaining = sizeof(tvar[0]) - 1;
+	while (*src) {
+		int len = encoding->mblen(*src);
+		if (len > remaining)
+			break;
+		memcpy(dst, src, len);
+		src += len;
+		dst += len;
+		remaining -= len;
+	}
+	*dst = '\0';
+}
+
 // WinMainとのインターフェース
 
 int NACT::get_screen_height()
diff --git a/src/sys/nact.h b/src/sys/nact.h
index d04c67a..f1ec3a5 100644
--- a/src/sys/nact.h
+++ b/src/sys/nact.h
@@ -80,6 +80,7 @@
 #define MAX_VERB 128
 #define MAX_OBJ 256
 #define MAX_PCM 256
+#define MAX_VAR 512
 #define MAX_STRVAR 10
 
 class AGS;
@@ -109,7 +110,7 @@ protected:
 	void execute();
 
 	// 変数
-	uint16 var[512] = {};
+	uint16 var[MAX_VAR] = {};
 	uint16 var_stack[30][20] = {};
 	char tvar[MAX_STRVAR][33] = {};
 	char tvar_stack[30][MAX_STRVAR][22] = {};
@@ -229,6 +230,8 @@ public:
 	int mainloop();
 	void sys_sleep(int ms);
 	void quit(int code);
+	void process_next_event();
+	bool is_terminating() const { return terminate; }
 
 	int get_screen_height();
 
@@ -250,10 +253,13 @@ public:
 
 	int get_scenario_page() const { return sco.page(); }
 	uint16 get_var(int index) const { return var[index]; }
+	void set_var(int index, uint16_t value) { var[index] = value; }
 	const char* get_string(int index) const { return tvar[index]; }
+	void set_string(int index, const char* value);
 
 private:
 	void pump_events();
+	void handle_event(SDL_Event e);
 	bool handle_platform_event(const SDL_Event& e);
 };
 
diff --git a/src/sys/nact_input.cpp b/src/sys/nact_input.cpp
index 82a7bf9..c8e4fb9 100644
--- a/src/sys/nact_input.cpp
+++ b/src/sys/nact_input.cpp
@@ -12,6 +12,7 @@
 #include "nact.h"
 #include "ags.h"
 #include "texthook.h"
+#include "debugger/debugger.h"
 
 enum TouchState {
 	TOUCH_NONE,
@@ -23,65 +24,89 @@ extern SDL_Window* g_window;
 static int mousex, mousey;
 static TouchState touch_state = TOUCH_NONE;
 
+void NACT::handle_event(SDL_Event e)
+{
+	if (handle_platform_event(e))
+		return;
+
+	switch (e.type) {
+	case SDL_QUIT:
+		quit(0);
+		break;
+
+	case SDL_WINDOWEVENT:
+		switch (e.window.event) {
+		case SDL_WINDOWEVENT_EXPOSED:
+		case SDL_WINDOWEVENT_SIZE_CHANGED:
+			ags->flush_screen(false);
+			break;
+		}
+		break;
+
+	case SDL_MOUSEMOTION:
+		mousex = e.motion.x * ags->screen_width / ags->window_width;
+		mousey = e.motion.y * ags->screen_height / ags->window_height;
+		break;
+
+	case SDL_FINGERDOWN:
+	case SDL_FINGERUP:
+	case SDL_FINGERMOTION:
+		mousex = e.tfinger.x * ags->screen_width;
+		mousey = e.tfinger.y * ags->screen_height;
+		switch (SDL_GetNumTouchFingers(e.tfinger.touchId)) {
+		case 0:
+			touch_state = TOUCH_NONE;
+			break;
+		case 1:
+			// A touch outside of the viewport (SDL clamps it to 0.0-1.0) is
+			// a right-click.
+			if (e.tfinger.x == 0.0f || e.tfinger.x == 1.0f ||
+				e.tfinger.y == 0.0f || e.tfinger.y == 1.0f) {
+				touch_state = TOUCH_RBUTTON;
+			} else {
+				touch_state = TOUCH_LBUTTON;
+			}
+			break;
+		case 2:
+			// Two-finger touch is a right-click.
+			touch_state = TOUCH_RBUTTON;
+			break;
+		}
+		break;
+
+	case SDL_APP_DIDENTERFOREGROUND:
+		ags->flush_screen(false);
+		break;
+
+	default:
+#ifdef ENABLE_DEBUGGER
+		if (e.type == sdl_custom_event_type) {
+			switch (e.user.code) {
+			case DEBUGGER_COMMAND:
+				g_debugger->post_command(e.user.data1);
+				break;
+			}
+		}
+#endif
+		break;
+	}
+}
+
 void NACT::pump_events()
 {
 	SDL_Event e;
 	while (SDL_PollEvent(&e)) {
-		if (handle_platform_event(e))
-			continue;
-
-		switch (e.type) {
-		case SDL_QUIT:
-			quit(0);
-			break;
-
-		case SDL_WINDOWEVENT:
-			switch (e.window.event) {
-			case SDL_WINDOWEVENT_EXPOSED:
-			case SDL_WINDOWEVENT_SIZE_CHANGED:
-				ags->flush_screen(false);
-				break;
-			}
-			break;
-
-		case SDL_MOUSEMOTION:
-			mousex = e.motion.x * ags->screen_width / ags->window_width;
-			mousey = e.motion.y * ags->screen_height / ags->window_height;
-			break;
-
-		case SDL_FINGERDOWN:
-		case SDL_FINGERUP:
-		case SDL_FINGERMOTION:
-			mousex = e.tfinger.x * ags->screen_width;
-			mousey = e.tfinger.y * ags->screen_height;
-			switch (SDL_GetNumTouchFingers(e.tfinger.touchId)) {
-			case 0:
-				touch_state = TOUCH_NONE;
-				break;
-			case 1:
-				// A touch outside of the viewport (SDL clamps it to 0.0-1.0) is
-				// a right-click.
-				if (e.tfinger.x == 0.0f || e.tfinger.x == 1.0f ||
-					e.tfinger.y == 0.0f || e.tfinger.y == 1.0f) {
-					touch_state = TOUCH_RBUTTON;
-				} else {
-					touch_state = TOUCH_LBUTTON;
-				}
-				break;
-			case 2:
-				// Two-finger touch is a right-click.
-				touch_state = TOUCH_RBUTTON;
-				break;
-			}
-			break;
-
-		case SDL_APP_DIDENTERFOREGROUND:
-			ags->flush_screen(false);
-			break;
-		}
+		handle_event(std::move(e));
 	}
 }
 
+void NACT::process_next_event()
+{
+	SDL_Event e;
+	SDL_WaitEvent(&e);
+	handle_event(std::move(e));
+}
+
 uint8 NACT::get_key()
 {
 	uint8 val = 0;
diff --git a/src/win/nact_win.cpp b/src/win/nact_win.cpp
index 76c9961..3f479f9 100644
--- a/src/win/nact_win.cpp
+++ b/src/win/nact_win.cpp
@@ -10,6 +10,7 @@
 #include "msgskip.h"
 #include "texthook.h"
 #include "resource.h"
+#include "debugger/debugger.h"
 
 extern SDL_Window* g_window;
 
@@ -150,6 +151,16 @@ void NACT::platform_finalize()
 
 void NACT::output_console(const char *format, ...)
 {
+#ifdef ENABLE_DEBUGGER
+	if (g_debugger) {
+		va_list ap;
+		va_start(ap, format);
+		bool handled = g_debugger->console_vprintf(format, ap);
+		va_end(ap);
+		if (handled)
+			return;
+	}
+#endif
 #if defined(_DEBUG_CONSOLE)
 	va_list ap;