diff --git a/.github/workflows/linux.yml b/.github/workflows/linux.yml
index 10683a4..e324553 100644
--- a/.github/workflows/linux.yml
+++ b/.github/workflows/linux.yml
@@ -15,7 +15,7 @@ jobs:
     - name: Install Deps
       run: |
         sudo apt update
-        sudo apt install libgtk-3-dev libsdl2-dev libsdl2-ttf-dev libsdl2-mixer-dev libportmidi-dev
+        sudo apt install libgtk-3-dev libsdl2-dev libsdl2-ttf-dev libsdl2-mixer-dev libportmidi-dev libcjson-dev
 
     - name: Build
       run: |
diff --git a/.github/workflows/windows.yml b/.github/workflows/windows.yml
index d2aa2e7..62f5467 100644
--- a/.github/workflows/windows.yml
+++ b/.github/workflows/windows.yml
@@ -33,7 +33,7 @@ jobs:
         echo PATH: $PATH
 
     - name: Install Deps
-      run: pacman -S --noconfirm ${{ matrix.package }}-SDL2 ${{ matrix.package }}-SDL2_ttf ${{ matrix.package }}-SDL2_mixer ${{ matrix.package }}-libjpeg-turbo ${{ matrix.package }}-nsis ${{ matrix.package }}-ntldd-git
+      run: pacman -S --noconfirm ${{ matrix.package }}-SDL2 ${{ matrix.package }}-SDL2_ttf ${{ matrix.package }}-SDL2_mixer ${{ matrix.package }}-libjpeg-turbo ${{ matrix.package }}-cjson ${{ matrix.package }}-nsis ${{ matrix.package }}-ntldd-git
 
     - name: Checkout
       uses: actions/checkout@v2
diff --git a/CMakeLists.txt b/CMakeLists.txt
index abb61f0..f86eb2d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -49,6 +49,16 @@ else()
   optional_pkg_check_modules(SDL2MIXER IMPORTED_TARGET SDL2_mixer)
 
   option(ENABLE_DEBUGGER "Enable built-in debugger" ON)
+  if (ENABLE_DEBUGGER)
+    pkg_check_modules(cJSON IMPORTED_TARGET libcjson)
+    if (NOT cJSON_FOUND)
+      # libcjson-dev of Debian buster / Ubuntu 20.04 does not install pkgconfig files.
+      find_library(cJSON cjson)
+      if (NOT cJSON)
+        message(FATAL_ERROR "libcjson is required but not found.")
+      endif()
+    endif()
+  endif()
 
   include(FindJPEG)
   if (JPEG_FOUND)
diff --git a/README.md b/README.md
index 94e50e6..3a1582c 100644
--- a/README.md
+++ b/README.md
@@ -8,7 +8,7 @@ Prebuilt binaries for Windows and Android can be downloaded from the [Releases](
 ## Build
 ### Linux (Debian / Ubuntu)
 
-    $ sudo apt install build-essential cmake libgtk-3-dev libsdl2-dev libsdl2-ttf-dev libsdl2-mixer-dev
+    $ sudo apt install build-essential cmake libgtk-3-dev libsdl2-dev libsdl2-ttf-dev libsdl2-mixer-dev libcjson-dev
     $ mkdir -p out/debug
     $ cd out/debug
     $ cmake -DCMAKE_BUILD_TYPE=Debug ../../
@@ -18,7 +18,7 @@ Prebuilt binaries for Windows and Android can be downloaded from the [Releases](
 
 [Homebrew](https://brew.sh/index_ja) is needed.
 
-    $ brew install cmake pkg-config sdl2 sdl2_mixer sdl2_ttf libjpeg
+    $ brew install cmake pkg-config sdl2 sdl2_mixer sdl2_ttf libjpeg cjson
     $ mkdir -p out/debug
     $ cd out/debug
     $ cmake -DCMAKE_BUILD_TYPE=Debug ../../
@@ -28,7 +28,7 @@ Prebuilt binaries for Windows and Android can be downloaded from the [Releases](
 
 [MSYS2](https://www.msys2.org) is needed.
 
-    $ pacman -S cmake mingw-w64-x86_64-cmake mingw-w64-x86_64-SDL2 mingw-w64-x86_64-SDL2_ttf mingw-w64-x86_64-SDL2_mixer mingw-w64-x86_64-libjpeg-turbo
+    $ pacman -S cmake mingw-w64-x86_64-cmake mingw-w64-x86_64-SDL2 mingw-w64-x86_64-SDL2_ttf mingw-w64-x86_64-SDL2_mixer mingw-w64-x86_64-libjpeg-turbo mingw-w64-x86_64-cjson
     $ mkdir -p out/debug
     $ cd out/debug
     $ cmake -G"MSYS Makefiles" -DCMAKE_BUILD_TYPE=Debug ../../
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 51c1ec7..924f6f3 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -71,7 +71,7 @@ target_sources(xsystem35 PRIVATE
 # Debugger
 if (ENABLE_DEBUGGER)
   target_sources(xsystem35 PRIVATE
-    debug_symbol.c debugger.c debugger_cui.c)
+    debug_symbol.c debugger.c debugger_cui.c debugger_dap.c)
 endif()
 
 if (WIN32)
@@ -116,6 +116,13 @@ else()  # non-emscripten, non-android
   if (SDL2MIXER_FOUND)
     target_link_libraries(xsystem35 PRIVATE PkgConfig::SDL2MIXER)
   endif()
+  if (ENABLE_DEBUGGER)
+    if (cJSON_FOUND)
+      target_link_libraries(xsystem35 PRIVATE PkgConfig::cJSON)
+    else()
+      target_link_libraries(xsystem35 PRIVATE ${cJSON})
+    endif()
+  endif()
 
   install(TARGETS xsystem35 RUNTIME DESTINATION bin)
 
diff --git a/src/debugger.c b/src/debugger.c
index 4ce335f..eb8dc61 100644
--- a/src/debugger.c
+++ b/src/debugger.c
@@ -31,6 +31,7 @@
 #define INTERNAL_BREAKPOINT_NO -1
 
 DebuggerState dbg_state = DBG_RUNNING;
+DebuggerImpl *dbg_impl;
 
 struct debug_symbols *symbols;
 static Breakpoint *breakpoints = NULL;
@@ -43,12 +44,17 @@ static struct {
 	int line;
 } step_exec_state;
 
-void dbg_init(const char *symbols_path) {
-	dbg_cui_init();
+void dbg_init(const char *symbols_path, boolean use_dap) {
+	dbg_impl = use_dap ? &dbg_dap_impl : &dbg_cui_impl;
+	dbg_impl->init();
 	dbg_state = DBG_STOPPED_ENTRY;
 	symbols = dsym_load(symbols_path);
 }
 
+void dbg_quit() {
+	dbg_impl->quit();
+}
+
 int dbg_lookup_var(const char *name) {
 	if (symbols)
 		return dsym_lookup_variable(symbols, name);
@@ -113,6 +119,26 @@ boolean dbg_delete_breakpoint(int no) {
 	return false;
 }
 
+void dbg_delete_breakpoints_in_page(int page) {
+	Breakpoint *prev = NULL;
+	for (Breakpoint *bp = breakpoints; bp;) {
+		if (bp->page == page) {
+			assert(bp->dfile->data[bp->addr] == BREAKPOINT);
+			bp->dfile->data[bp->addr] = bp->restore_op;
+			ald_freedata(bp->dfile);
+			if (prev)
+				prev->next = bp->next;
+			else
+				breakpoints = bp->next;
+			bp = bp->next;
+			free(bp);
+		} else {
+			prev = bp;
+			bp = bp->next;
+		}
+	}
+}
+
 BYTE dbg_handle_breakpoint(int page, int addr) {
 	Breakpoint *bp = dbg_find_breakpoint(page, addr);
 	if (!bp)
@@ -265,5 +291,10 @@ void dbg_main(void) {
 	default:
 		break;
 	}
-	dbg_cui_repl();
+	dbg_impl->repl();
+}
+
+void dbg_onsleep(void) {
+	if (dbg_impl)
+		dbg_impl->onsleep();
 }
diff --git a/src/debugger.h b/src/debugger.h
index c5274e3..4045cad 100644
--- a/src/debugger.h
+++ b/src/debugger.h
@@ -39,17 +39,19 @@ extern DebuggerState dbg_state;
 #ifdef ENABLE_DEBUGGER
 
 #define dbg_trapped() (dbg_state != DBG_RUNNING)
-#define dbg_interrupted() (dbg_state == DBG_STOPPED_INTERRUPT)
-void dbg_init(const char *symbols_path);
+void dbg_init(const char *symbols_path, boolean use_dap);
+void dbg_quit();
 void dbg_main(void);
+void dbg_onsleep(void);
 BYTE dbg_handle_breakpoint(int page, int addr);
 
 #else // ENABLE_DEBUGGER
 
 #define dbg_trapped() false
-#define dbg_interrupted() false
-#define dbg_init(symbols_path)
+#define dbg_init(symbols_path, use_dap)
+#define dbg_quit()
 #define dbg_main()
+#define dbg_onsleep()
 #define dbg_handle_breakpoint(page, addr) BREAKPOINT
 
 #endif // ENABLE_DEBUGGER
diff --git a/src/debugger_cui.c b/src/debugger_cui.c
index a51dcd8..0c5c5eb 100644
--- a/src/debugger_cui.c
+++ b/src/debugger_cui.c
@@ -315,7 +315,7 @@ static void sigint_handler(int sig_num) {
 	dbg_state = DBG_STOPPED_INTERRUPT;
 }
 
-void dbg_cui_init(void) {
+static void dbg_cui_init(void) {
 #ifdef HAVE_SIGACTION
 	sys_set_signalhandler(SIGINT, sigint_handler);
 #endif
@@ -325,6 +325,9 @@ void dbg_cui_init(void) {
 #endif
 }
 
+static void dbg_cui_quit(void) {
+}
+
 typedef struct {
 	const char *name;
 	const char *alias;
@@ -379,7 +382,7 @@ static CommandResult cmd_help(void) {
 	return CONTINUE_REPL;
 }
 
-void dbg_cui_repl(void) {
+static void dbg_cui_repl(void) {
 	if (dbg_state == DBG_STOPPED_BREAKPOINT) {
 		Breakpoint *bp = dbg_find_breakpoint(nact->current_page, nact->current_addr);
 		if (bp)
@@ -408,3 +411,15 @@ void dbg_cui_repl(void) {
 		}
 	}
 }
+
+static void dbg_cui_onsleep(void) {
+	if (dbg_state == DBG_STOPPED_INTERRUPT)
+		dbg_main();
+}
+
+DebuggerImpl dbg_cui_impl = {
+	.init = dbg_cui_init,
+	.quit = dbg_cui_quit,
+	.repl = dbg_cui_repl,
+	.onsleep = dbg_cui_onsleep,
+};
diff --git a/src/debugger_dap.c b/src/debugger_dap.c
new file mode 100644
index 0000000..5cd65c7
--- /dev/null
+++ b/src/debugger_dap.c
@@ -0,0 +1,450 @@
+/*
+ * Copyright (C) 2021 kichikuou <KichikuouChrome@gmail.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ *
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <SDL_mutex.h>
+#include <SDL_thread.h>
+#ifdef _WIN32
+#include <fcntl.h>
+#include <io.h>
+#endif
+
+#include "cjson/cJSON.h"
+#include "debugger.h"
+#include "debugger_private.h"
+#include "debug_symbol.h"
+#include "system.h"
+#include "variable.h"
+
+#define THREAD_ID 1
+
+static boolean initialized = false;
+static char *src_dir;
+
+cJSON *create_source(const char *name) {
+	cJSON *source = cJSON_CreateObject();
+	cJSON_AddStringToObject(source, "name", name);
+	if (src_dir) {
+		char *buf = alloca(strlen(src_dir) + strlen(name) + 2);
+		sprintf(buf, "%s/%s", src_dir, name);
+		cJSON_AddStringToObject(source, "path", buf);
+	}
+	cJSON_AddNumberToObject(source, "sourceReference", 0);
+	return source;
+}
+
+static void send_json(cJSON *json) {
+	static int seq = 0;
+
+	cJSON_AddNumberToObject(json, "seq", seq);
+	char *str = cJSON_PrintUnformatted(json);
+	printf("Content-Length: %zu\r\n\r\n%s", strlen(str), str);
+	fflush(stdout);
+	free(str);
+	cJSON_free(json);
+}
+
+static void emit_initialized_event() {
+	cJSON *event = cJSON_CreateObject();
+	cJSON_AddStringToObject(event, "type", "event");
+	cJSON_AddStringToObject(event, "event", "initialized");
+	send_json(event);
+}
+
+static void emit_terminated_event() {
+	cJSON *event = cJSON_CreateObject();
+	cJSON_AddStringToObject(event, "type", "event");
+	cJSON_AddStringToObject(event, "event", "terminated");
+	send_json(event);
+}
+
+static void emit_stop_event() {
+	const char *reason;
+	switch (dbg_state) {
+	case DBG_STOPPED_ENTRY: reason = "entry"; break;
+	case DBG_STOPPED_STEP: reason = "step"; break;
+	case DBG_STOPPED_NEXT: reason = "step"; break;
+	case DBG_STOPPED_BREAKPOINT: reason = "breakpoint"; break;
+	case DBG_STOPPED_INTERRUPT: reason = "pause"; break;
+	default: reason = "unknown"; break;
+	}
+
+	cJSON *event = cJSON_CreateObject(), *body;
+	cJSON_AddStringToObject(event, "type", "event");
+	cJSON_AddStringToObject(event, "event", "stopped");
+	cJSON_AddItemToObjectCS(event, "body", body = cJSON_CreateObject());
+	cJSON_AddStringToObject(body, "reason", reason);
+	cJSON_AddNumberToObject(body, "threadId", THREAD_ID);  // needed?
+	send_json(event);
+}
+
+static void cmd_initialize(cJSON *args, cJSON *resp) {
+	cJSON *body;
+	cJSON_AddBoolToObject(resp, "success", true);
+	cJSON_AddItemToObjectCS(resp, "body", body = cJSON_CreateObject());
+	cJSON_AddBoolToObject(body, "supportsConfigurationDoneRequest", true);
+	cJSON_AddBoolToObject(body, "supportsEvaluateForHovers", true);
+}
+
+static void cmd_launch(cJSON *args, cJSON *resp) {
+	cJSON *srcDir = cJSON_GetObjectItemCaseSensitive(args, "srcDir");
+	if (cJSON_IsString(srcDir))
+		src_dir = strdup(srcDir->valuestring);
+	cJSON_AddBoolToObject(resp, "success", true);
+
+	emit_initialized_event();
+	initialized = true;
+}
+
+static void cmd_configurationDone(cJSON *args, cJSON *resp) {
+	cJSON_AddBoolToObject(resp, "success", true);
+}
+
+static void cmd_stackTrace(cJSON *args, cJSON *resp) {
+	StackTrace *trace = dbg_stack_trace();
+
+	cJSON *body, *stackFrames;
+	cJSON_AddBoolToObject(resp, "success", true);
+	cJSON_AddItemToObjectCS(resp, "body", body = cJSON_CreateObject());
+	cJSON_AddItemToObjectCS(body, "stackFrames", stackFrames = cJSON_CreateArray());
+	for (int i = 0; i < trace->nr_frame; i++) {
+		StackFrame *frame = &trace->frames[i];
+		cJSON *item = cJSON_CreateObject();
+		cJSON_AddItemToArray(stackFrames, item);
+		cJSON_AddNumberToObject(item, "id", i);
+		cJSON_AddStringToObject(item, "name", frame->name);
+		cJSON_AddItemToObjectCS(item, "source", create_source(frame->src));
+		cJSON_AddNumberToObject(item, "line", frame->line);
+		cJSON_AddNumberToObject(item, "column", 0);
+	}
+	cJSON_AddNumberToObject(body, "totalFrames", trace->nr_frame);
+
+	free(trace);
+}
+
+static void cmd_setBreakpoints(cJSON *args, cJSON *resp) {
+	cJSON *source = cJSON_GetObjectItemCaseSensitive(args, "source");
+	cJSON *source_name = cJSON_GetObjectItemCaseSensitive(source, "name");
+	cJSON *lines = cJSON_GetObjectItemCaseSensitive(args, "lines");
+	if (!cJSON_IsString(source_name) || !cJSON_IsArray(lines)) {
+		cJSON_AddBoolToObject(resp, "success", false);
+		// TODO: add message
+		return;
+	}
+	const char *filename = source_name->valuestring;
+	int page = dsym_src2page(symbols, filename);
+
+	dbg_delete_breakpoints_in_page(page);
+
+	cJSON *body, *breakpoints;
+	cJSON_AddBoolToObject(resp, "success", true);
+	cJSON_AddItemToObjectCS(resp, "body", body = cJSON_CreateObject());
+	cJSON_AddItemToObjectCS(body, "breakpoints", breakpoints = cJSON_CreateArray());
+
+	cJSON *line;
+	cJSON_ArrayForEach(line, lines) {
+		cJSON *item = cJSON_CreateObject();
+		cJSON_AddItemToArray(breakpoints, item);
+
+		int line_no = line->valueint;
+		int addr = dsym_line2addr(symbols, page, line_no);
+		if (page < 0) {
+			fprintf(stderr, "No source file named %s.\n", filename);
+			cJSON_AddBoolToObject(item, "verified", false);
+			continue;
+		}
+		if (addr < 0) {
+			fprintf(stderr, "No line %d in file %s.\n", line_no, filename);
+			cJSON_AddBoolToObject(item, "verified", false);
+			continue;
+		}
+		Breakpoint *bp = dbg_set_breakpoint(page, addr, false);
+		if (!bp) {
+			fprintf(stderr, "Failed to set breakpoint at %d:0x%x\n", page, addr);
+			cJSON_AddBoolToObject(item, "verified", false);
+			continue;
+		}
+		line_no = dsym_addr2line(symbols, page, addr);
+		cJSON_AddNumberToObject(item, "id", bp->no);
+		cJSON_AddBoolToObject(item, "verified", true);
+		cJSON_AddItemToObjectCS(item, "source", create_source(filename));
+		cJSON_AddNumberToObject(item, "line", line_no);
+	}
+}
+
+static void cmd_evaluate(cJSON *args, cJSON *resp) {
+	cJSON *expression = cJSON_GetObjectItemCaseSensitive(args, "expression");
+	if (!cJSON_IsString(expression)) {
+		cJSON_AddBoolToObject(resp, "success", false);
+		// TODO: add message
+		return;
+	}
+	const char *varname = expression->valuestring;
+	int var = dbg_lookup_var(varname);
+	if (var < 0) {
+		fprintf(stderr, "Unrecognized variable name \"%s\".\n", varname);
+		// TODO: add message
+		cJSON_AddBoolToObject(resp, "success", false);
+		return;
+	}
+
+	char result[20];
+	sprintf(result, "%d", sysVar[var]);
+
+	cJSON *body;
+	cJSON_AddBoolToObject(resp, "success", true);
+	cJSON_AddItemToObjectCS(resp, "body", body = cJSON_CreateObject());
+	cJSON_AddStringToObject(body, "result", result);
+	cJSON_AddNumberToObject(body, "variablesReference", 0);
+}
+
+static void cmd_continue(cJSON *args, cJSON *resp) {
+	cJSON_AddBoolToObject(resp, "success", true);
+}
+
+static void cmd_pause(cJSON *args, cJSON *resp) {
+	dbg_state = DBG_STOPPED_INTERRUPT;
+	cJSON_AddBoolToObject(resp, "success", true);
+}
+
+static void cmd_stepIn(cJSON *args, cJSON *resp) {
+	dbg_step();
+	cJSON_AddBoolToObject(resp, "success", true);
+}
+
+static void cmd_next(cJSON *args, cJSON *resp) {
+	dbg_next();
+	cJSON_AddBoolToObject(resp, "success", true);
+}
+
+static void cmd_threads(cJSON *args, cJSON *resp) {
+	cJSON *body, *threads, *thread;
+	cJSON_AddBoolToObject(resp, "success", true);
+	cJSON_AddItemToObjectCS(resp, "body", body = cJSON_CreateObject());
+	cJSON_AddItemToObjectCS(body, "threads", threads = cJSON_CreateArray());
+	cJSON_AddItemToArray(threads, thread = cJSON_CreateObject());
+	cJSON_AddNumberToObject(thread, "id", THREAD_ID);
+	cJSON_AddStringToObject(thread, "name", "main thread");
+}
+
+static void cmd_scopes(cJSON *args, cJSON *resp) {
+	cJSON *body;
+	cJSON_AddBoolToObject(resp, "success", true);
+	cJSON_AddItemToObjectCS(resp, "body", body = cJSON_CreateObject());
+	cJSON_AddItemToObjectCS(body, "scopes", cJSON_CreateArray());
+}
+
+static void cmd_disconnect(cJSON *args, cJSON *resp) {
+	cJSON_AddBoolToObject(resp, "success", true);
+	send_json(resp);
+	sys_exit(0);
+}
+
+static boolean handle_request(cJSON *request) {
+	boolean continue_repl = true;
+
+	cJSON *resp = cJSON_CreateObject();
+	cJSON_AddStringToObject(resp, "type", "response");
+	cJSON *request_seq = cJSON_DetachItemFromObjectCaseSensitive(request, "seq");
+	cJSON_AddItemToObjectCS(resp, "request_seq", request_seq);
+	cJSON *command = cJSON_DetachItemFromObjectCaseSensitive(request, "command");
+	cJSON_AddItemToObjectCS(resp, "command", command);
+	cJSON *args = cJSON_GetObjectItemCaseSensitive(request, "arguments");
+
+	if (!cJSON_IsString(command)) {
+		fprintf(stderr, "protocol error: command is not a string\n");
+		// FIXME: return an error response
+		cJSON_free(resp);
+		return continue_repl;
+	}
+
+	if (!strcmp(command->valuestring, "initialize")) {
+		cmd_initialize(args, resp);
+	} else if (!strcmp(command->valuestring, "launch")) {
+		cmd_launch(args, resp);
+	} else if (!strcmp(command->valuestring, "configurationDone")) {
+		cmd_configurationDone(args, resp);
+	} else if (!strcmp(command->valuestring, "continue")) {
+		cmd_continue(args, resp);
+		continue_repl = false;
+	} else if (!strcmp(command->valuestring, "stackTrace")) {
+		cmd_stackTrace(args, resp);
+	} else if (!strcmp(command->valuestring, "stepIn")) {
+		cmd_stepIn(args, resp);
+		continue_repl = false;
+	} else if (!strcmp(command->valuestring, "next")) {
+		cmd_next(args, resp);
+		continue_repl = false;
+	} else if (!strcmp(command->valuestring, "pause")) {
+		cmd_pause(args, resp);
+	} else if (!strcmp(command->valuestring, "evaluate")) {
+		cmd_evaluate(args, resp);
+	} else if (!strcmp(command->valuestring, "setBreakpoints")) {
+		cmd_setBreakpoints(args, resp);
+	} else if (!strcmp(command->valuestring, "threads")) {
+		cmd_threads(args, resp);
+	} else if (!strcmp(command->valuestring, "scopes")) {
+		cmd_scopes(args, resp);
+	} else if (!strcmp(command->valuestring, "disconnect")) {
+		cmd_disconnect(args, resp);
+	} else {
+		fprintf(stderr, "unknown command \"%s\"\n", command->valuestring);
+	}
+	send_json(resp);
+	return continue_repl;
+}
+
+static boolean handle_message(char *msg) {
+	cJSON *json = cJSON_Parse(msg);
+	cJSON *type = cJSON_GetObjectItemCaseSensitive(json, "type");
+	boolean continue_repl = true;
+	if (cJSON_IsString(type) && !strcmp(type->valuestring, "request"))
+		continue_repl = handle_request(json);
+	cJSON_free(json);
+	free(msg);
+	return continue_repl;
+}
+
+struct cmdq_elem {
+	char *cmd;
+	struct cmdq_elem *next;
+};
+
+struct {
+	SDL_mutex *mutex;
+	SDL_cond *cond_nonempty;
+	struct cmdq_elem *head;
+	struct cmdq_elem *last;
+} cmd_queue;
+
+static boolean cmdq_isempty(void) {
+	return !cmd_queue.head;
+}
+
+static void cmdq_enqueue(char *cmd) {
+	struct cmdq_elem *e = malloc(sizeof(struct cmdq_elem));
+	e->cmd = cmd;
+	e->next = NULL;
+
+	SDL_LockMutex(cmd_queue.mutex);
+	if (!cmd_queue.head) {
+		cmd_queue.head = cmd_queue.last = e;
+	} else {
+		cmd_queue.last->next = e;
+		cmd_queue.last = e;
+	}
+	SDL_UnlockMutex(cmd_queue.mutex);
+	SDL_CondSignal(cmd_queue.cond_nonempty);
+}
+
+static char *cmdq_dequeue(void) {
+	SDL_LockMutex(cmd_queue.mutex);
+	while (!cmd_queue.head)
+		SDL_CondWait(cmd_queue.cond_nonempty, cmd_queue.mutex);
+
+	struct cmdq_elem *e = cmd_queue.head;
+	cmd_queue.head = e->next;
+	if (!e->next)
+		cmd_queue.last = NULL;
+
+	SDL_UnlockMutex(cmd_queue.mutex);
+
+	char *cmd = e->cmd;
+	free(e);
+	return cmd;
+}
+
+static int read_command_thread(void *data) {
+	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 = malloc(content_length);
+			fread(buf, content_length, 1, stdin);
+			cmdq_enqueue(buf);
+			content_length = -1;
+		} else {
+			fprintf(stderr, "Unknown Debug Adapter Protocol header: %s", header);
+		}
+	}
+	cmdq_enqueue(NULL);  // EOF
+	return 0;
+}
+
+static void dbg_dap_init(void) {
+	cmd_queue.mutex = SDL_CreateMutex();
+	cmd_queue.cond_nonempty = SDL_CreateCond();
+
+#ifdef _WIN32
+	_setmode(_fileno(stdin), _O_BINARY);
+	_setmode(_fileno(stdout), _O_BINARY);
+#endif
+
+	SDL_CreateThread(read_command_thread, "Debugger", NULL);
+
+	while (!initialized) {
+		char *msg = cmdq_dequeue();
+		if (!msg)
+			break;
+		handle_message(msg);
+	}
+}
+
+static void dbg_dap_quit(void) {
+	emit_terminated_event();
+}
+
+static void dbg_dap_repl(void) {
+	emit_stop_event();
+	dbg_state = DBG_RUNNING;
+
+	boolean continue_repl = true;
+	while (continue_repl) {
+		char *msg = cmdq_dequeue();
+		if (!msg)
+			break;
+		continue_repl = handle_message(msg);
+	}
+}
+
+static void dbg_dap_onsleep(void) {
+	while (!cmdq_isempty()) {
+		char *msg = cmdq_dequeue();
+		if (!msg)
+			break;
+		handle_message(msg);
+	}
+	if (dbg_state == DBG_STOPPED_INTERRUPT)
+		dbg_main();
+}
+
+DebuggerImpl dbg_dap_impl = {
+	.init = dbg_dap_init,
+	.quit = dbg_dap_quit,
+	.repl = dbg_dap_repl,
+	.onsleep = dbg_dap_onsleep,
+};
diff --git a/src/debugger_private.h b/src/debugger_private.h
index 95e4065..20cd767 100644
--- a/src/debugger_private.h
+++ b/src/debugger_private.h
@@ -47,14 +47,24 @@ typedef struct {
 	StackFrame frames[];
 } StackTrace;
 
+typedef struct {
+	void (*init)(void);
+	void (*quit)(void);
+	void (*repl)(void);
+	void (*onsleep)(void);
+} DebuggerImpl;
+
+extern DebuggerImpl dbg_cui_impl;
+extern DebuggerImpl dbg_dap_impl;
+extern DebuggerImpl *dbg_impl;
+
 Breakpoint *dbg_find_breakpoint(int page, int addr);
 Breakpoint *dbg_set_breakpoint(int page, int addr, boolean is_internal);
 boolean dbg_delete_breakpoint(int no);
+void dbg_delete_breakpoints_in_page(int page);
 void dbg_step(void);
 void dbg_next(void);
 int dbg_lookup_var(const char *name);
 StackTrace *dbg_stack_trace(void);
-void dbg_cui_init(void);
-void dbg_cui_repl(void);
 
 #endif // __DEBUGGER_PRIVATE_H__
diff --git a/src/sdl_draw.c b/src/sdl_draw.c
index d56836e..fe2f1e6 100644
--- a/src/sdl_draw.c
+++ b/src/sdl_draw.c
@@ -76,8 +76,7 @@ void sdl_updateScreen(void) {
 
 void sdl_sleep(int msec) {
 	sdl_updateScreen();
-	if (dbg_interrupted())
-		dbg_main();
+	dbg_onsleep();
 #ifdef __EMSCRIPTEN__
 	emscripten_sleep(msec);
 #else
@@ -97,8 +96,7 @@ EM_JS(void, wait_vsync, (void), {
 
 void sdl_wait_vsync() {
 	sdl_updateScreen();
-	if (dbg_interrupted())
-		dbg_main();
+	dbg_onsleep();
 #ifdef __EMSCRIPTEN__
 	wait_vsync();
 #else
diff --git a/src/xsystem35.c b/src/xsystem35.c
index e57b351..b2e6d7d 100644
--- a/src/xsystem35.c
+++ b/src/xsystem35.c
@@ -88,7 +88,11 @@ static void    check_profile();
 /* for debugging */
 static FILE *fpdebuglog;
 static int debuglv = DEBUGLEVEL;
-static boolean debugger_enabled;
+enum {
+	DEBUGGER_DISABLED,
+	DEBUGGER_CUI,
+	DEBUGGER_DAP,
+} debugger_mode = DEBUGGER_DISABLED;
 
 static int audio_buffer_size = 0;
 
@@ -246,6 +250,7 @@ static void sys35_init() {
 }
 
 static void sys35_remove() {
+	dbg_quit();
 	mus_exit(); 
 	ags_remove();
 #ifdef ENABLE_GTK
@@ -293,7 +298,9 @@ static void sys35_ParseOption(int *argc, char **argv) {
 			fclose(fp);
 			gameResourceFile = argv[i + 1];
 		} else if (0 == strcmp(argv[i], "-debug")) {
-			debugger_enabled = true;
+			debugger_mode = DEBUGGER_CUI;
+		} else if (0 == strcmp(argv[i], "-debug_dap")) {
+			debugger_mode = DEBUGGER_DAP;
 		} else if (0 == strcmp(argv[i], "-devcd")) {
 			if (argv[i + 1] != NULL) {
 				cd_set_devicename(argv[i + 1]);
@@ -455,7 +462,7 @@ static void registerGameFiles(void) {
 		SYSERROR("No Scenario data available\n");
 	for (int type = 0; type < DRIFILETYPEMAX; type++) {
 		boolean use_mmap = true;
-		if (debugger_enabled && type == DRIFILE_SCO) {
+		if (debugger_mode != DEBUGGER_DISABLED && type == DRIFILE_SCO) {
 			// Do not mmap scenario files so that BREAKPOINT instructions can be inserted.
 			use_mmap = false;
 		}
@@ -525,10 +532,10 @@ int main(int argc, char **argv) {
 #endif
 	menu_init();
 	
-	if (debugger_enabled) {
+	if (debugger_mode != DEBUGGER_DISABLED) {
 		char symbols_path[500];
 		snprintf(symbols_path, sizeof(symbols_path), "%s.symbols", nact->files.game_fname[DRIFILE_SCO][0]);
-		dbg_init(symbols_path);
+		dbg_init(symbols_path, debugger_mode == DEBUGGER_DAP);
 	}
 
 	nact_main();