diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index a7ec5ba..8975ecb 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -19,7 +19,7 @@ project(${APP_NAME}
     LANGUAGES C
 )
 
-add_executable(${APP_NAME} main.c utils.c buffer.c backtrace.c)
+add_executable(${APP_NAME} main.c utils.c buffer.c backtrace.c monitor.c client.c)
 
 # use C23
 set_property(TARGET ${APP_NAME} PROPERTY C_STANDARD 23)
@@ -31,6 +31,9 @@ pkg_check_modules(deps REQUIRED
 
     xcb
     xcb-aux
+    xcb-randr
+    xcb-xfixes
+    xcb-xinerama
 )
 
 target_include_directories(${APP_NAME} SYSTEM
diff --git a/src/bar.h b/src/bar.h
new file mode 100644
index 0000000..3f59c93
--- /dev/null
+++ b/src/bar.h
@@ -0,0 +1,2 @@
+#pragma once
+
diff --git a/src/base.h b/src/base.h
new file mode 100644
index 0000000..a748914
--- /dev/null
+++ b/src/base.h
@@ -0,0 +1,13 @@
+#pragma once
+
+#include <stdint.h>
+
+typedef struct area_t {
+  int16_t x, y;
+  uint16_t width, height;
+} area_t;
+
+typedef struct extent_in_bar_t {
+  int16_t start;
+  int16_t end;
+} extent_in_bar_t;
diff --git a/src/client.c b/src/client.c
new file mode 100644
index 0000000..a8c4739
--- /dev/null
+++ b/src/client.c
@@ -0,0 +1,17 @@
+#include "client.h"
+
+void client_scan(void) {}
+void client_focus(client_t *client) {}
+void client_stack_raise(client_t *client) {}
+void client_move_to(client_t *client, int16_t x, int16_t y) {}
+void client_resize(client_t *client, uint16_t width, uint16_t height) {}
+void client_change_border_color(client_t *client, color_t *color) {}
+void client_change_border_width(client_t *client, uint16_t border_width) {}
+void client_set_floating(client_t *client, bool floating) {}
+void client_set_fullscreen(client_t *client, bool fullscreen) {}
+void client_set_maximize(client_t *client, bool maximize) {}
+void client_set_minimize(client_t *client, bool minimize) {}
+void client_set_class_instance(client_t *client, const char *class,
+                               const char *instance) {}
+bool client_is_visible(client_t *client) { return false; }
+void client_send_to_tag(client_t *client, tag_t *tag) {}
diff --git a/src/client.h b/src/client.h
new file mode 100644
index 0000000..603b67d
--- /dev/null
+++ b/src/client.h
@@ -0,0 +1,22 @@
+#pragma once
+
+#include <stdint.h>
+
+#include "color.h"
+#include "types.h"
+
+void client_scan(void);
+void client_focus(client_t *client);
+void client_stack_raise(client_t *client);
+void client_move_to(client_t *client, int16_t x, int16_t y);
+void client_resize(client_t *client, uint16_t width, uint16_t height);
+void client_change_border_color(client_t *client, color_t *color);
+void client_change_border_width(client_t *client, uint16_t border_width);
+void client_set_floating(client_t *client, bool floating);
+void client_set_fullscreen(client_t *client, bool fullscreen);
+void client_set_maximize(client_t *client, bool maximize);
+void client_set_minimize(client_t *client, bool minimize);
+void client_set_class_instance(client_t *client, const char *class,
+                               const char *instance);
+bool client_is_visible(client_t *client);
+void client_send_to_tag(client_t *client, tag_t *tag);
diff --git a/src/color.h b/src/color.h
new file mode 100644
index 0000000..746261c
--- /dev/null
+++ b/src/color.h
@@ -0,0 +1,22 @@
+#pragma once
+
+#include <stdint.h>
+
+typedef struct color_t {
+  uint32_t rgba; /* use for human reading */
+  uint32_t argb; /* use for xcb */
+
+  /* channels of color, use for cairo */
+  double red;   /* red channel */
+  double green; /* green channel */
+  double blue;  /* blue channel */
+  double alpha; /* alpha channel */
+} color_t;
+
+/**
+ * @brief parsing color represented in hexadecimal format
+ * @param hex color represented in hexadecimal format, the supported format
+   have: RGB/RGBA/RRGGBB/RRGGBBAA/#RGB/#RGBA/#RRGGBB/#RRGGBBAA
+ * @param color return the parsed color
+ */
+void parse_color(const char *hex, color_t *const color);
diff --git a/src/draw.h b/src/draw.h
new file mode 100644
index 0000000..45dcbb0
--- /dev/null
+++ b/src/draw.h
@@ -0,0 +1,3 @@
+#pragma once
+
+
diff --git a/src/main.c b/src/main.c
index 18dbf8a..9ea6cc6 100644
--- a/src/main.c
+++ b/src/main.c
@@ -2,15 +2,22 @@
 #include <glib.h>
 #include <glibconfig.h>
 #include <signal.h>
+#include <stdint.h>
+#include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
+#include <xcb/randr.h>
 #include <xcb/xcb.h>
 #include <xcb/xcb_aux.h>
+#include <xcb/xfixes.h>
+#include <xcb/xinerama.h>
 #include <xcb/xproto.h>
 
 #include "backtrace.h"
 #include "buffer.h"
+#include "client.h"
+#include "monitor.h"
 #include "types.h"
 #include "utils.h"
 
@@ -82,6 +89,22 @@ static void check_other_wm(void) {
   global_state.screen = screen;
 }
 
+static void check_xcb_extensions(void) {
+  xcb_prefetch_extension_data(global_state.xcb_conn, &xcb_xfixes_id);
+  xcb_prefetch_extension_data(global_state.xcb_conn, &xcb_xinerama_id);
+  xcb_prefetch_extension_data(global_state.xcb_conn, &xcb_randr_id);
+
+  const xcb_query_extension_reply_t *query;
+  query = xcb_get_extension_data(global_state.xcb_conn, &xcb_xfixes_id);
+  global_state.have_xfixes = query && query->present;
+
+  query = xcb_get_extension_data(global_state.xcb_conn, &xcb_xinerama_id);
+  global_state.have_xinerama = query && query->present;
+
+  query = xcb_get_extension_data(global_state.xcb_conn, &xcb_randr_id);
+  global_state.have_randr = query && query->present;
+}
+
 int main(int argc, char *argv[]) {
   p_clear(&global_state, 1);
 
@@ -105,6 +128,10 @@ int main(int argc, char *argv[]) {
   sigaction(SIGCHLD, &sa, 0);
 
   check_other_wm();
+  check_xcb_extensions();
+
+  monitor_scan();
+  client_scan();
 
   if (global_state.loop == NULL) {
     global_state.loop = g_main_loop_new(NULL, FALSE);
diff --git a/src/monitor.c b/src/monitor.c
new file mode 100644
index 0000000..0260f74
--- /dev/null
+++ b/src/monitor.c
@@ -0,0 +1,5 @@
+#include "monitor.h"
+
+void monitor_scan(void) {}
+
+void monitor_draw_bar(monitor_t *monitor) {}
diff --git a/src/monitor.h b/src/monitor.h
new file mode 100644
index 0000000..42cc4de
--- /dev/null
+++ b/src/monitor.h
@@ -0,0 +1,6 @@
+#pragma once
+
+#include "types.h"
+
+void monitor_scan(void);
+void monitor_draw_bar(monitor_t *monitor);
diff --git a/src/types.h b/src/types.h
index 00e6320..9e96fca 100644
--- a/src/types.h
+++ b/src/types.h
@@ -1,16 +1,85 @@
 #pragma once
 
 #include <glib.h>
+#include <stdint.h>
 #include <xcb/xcb.h>
 #include <xcb/xproto.h>
 
+#include "base.h"
+#include "color.h"
+
+typedef struct client_t client_t;
+typedef struct monitor_t monitor_t;
+typedef struct tag_t tag_t;
+typedef struct task_in_tag_t task_in_tag_t;
+
+struct client_t {
+  client_t *stack_next;
+  client_t *next;
+  tag_t *tag;
+
+  area_t geometry;
+  color_t border_color;
+  uint16_t border_width;
+
+  bool floating;
+  bool fullscreen;
+  bool maximize;
+  bool minimize;
+  bool sticky;
+
+  char *name;
+  char *class;
+  char *instance;
+
+  xcb_window_t transient_for_window;
+  xcb_window_t frame_window;
+  xcb_window_t window;
+};
+
+struct monitor_t {
+  monitor_t *next;
+  area_t geometry;
+  area_t workarea;
+  tag_t *tag_list;
+  tag_t *selected_tag;
+
+  xcb_window_t bar_window;
+};
+
+struct tag_t {
+  uint32_t index; /* index in all tags */
+  uint32_t mask;
+  extent_in_bar_t bar_extent;
+  tag_t *next;
+  char *name;
+  monitor_t *monitor;
+  task_in_tag_t *task_list;
+};
+
+struct task_in_tag_t {
+  client_t *client;
+  task_in_tag_t *next;
+  area_t geometry;
+  extent_in_bar_t bar_extent;
+};
+
 typedef struct global_state_t {
   bool need_restart;
   GMainLoop *loop;
 
+  client_t *client_list;
+  client_t *client_stack_list;
+  client_t *client_focused;
+  monitor_t *monitor_list;
+  monitor_t *current_monitor;
+
   xcb_connection_t *xcb_conn;
   xcb_screen_t *screen;
   int default_screen;
+  bool have_xfixes;
+  bool have_xinerama;
+  bool have_randr;
 } global_state_t;
 
 extern global_state_t global_state;
diff --git a/src/xwindow.h b/src/xwindow.h
new file mode 100644
index 0000000..6f70f09
--- /dev/null
+++ b/src/xwindow.h
@@ -0,0 +1 @@
+#pragma once