diff --git a/cmd/main.cfg.json b/cmd/main.cfg.json
new file mode 100644
index 0000000..287a602
--- /dev/null
+++ b/cmd/main.cfg.json
@@ -0,0 +1,7 @@
+{
+	"WindowWidth":  1600,
+	"WindowHeight": 900,
+
+	"FramerateLimit": 60
+}
+
diff --git a/cmd/main.go b/cmd/main.go
index ca4181e..7a7f0ad 100644
--- a/cmd/main.go
+++ b/cmd/main.go
@@ -13,34 +13,48 @@ import (
 	"github.com/go-gl/glfw/v3.3/glfw"
 )
 
-const (
-	//windowWidth  = 852
-	//windowHeight = 480
-	windowWidth  = 1600
-	windowHeight = 900
+var (
+	frameTick *time.Ticker
 )
 
+
 func init() {
 	runtime.LockOSThread()
 }
+
 func main() {
 
+	err := gio.LoadConfig()
+	if err != nil {
+		panic(err)
+	}
+
 	if err := glfw.Init(); err != nil {
 		panic(err)
 	}
 	defer glfw.Terminate()
 
+	// framerate limit ticker
+	if gio.MainConfig.FramerateLimit > 0 {
+		frameTick = time.NewTicker(time.Second / time.Duration(gio.MainConfig.FramerateLimit))
+	}
+
 	glfw.WindowHint(glfw.Resizable, 1)
 	glfw.WindowHint(glfw.ContextVersionMajor, 3)
 	glfw.WindowHint(glfw.ContextVersionMinor, 3)
 	glfw.WindowHint(glfw.OpenGLProfile, glfw.OpenGLCoreProfile)
 	glfw.WindowHint(glfw.OpenGLForwardCompatible, 1)
-	win, err := glfw.CreateWindow(windowWidth, windowHeight, "Gl01", nil, nil)
+	win, err := glfw.CreateWindow(gio.MainConfig.WindowWidth, gio.MainConfig.WindowHeight, "Gl01", nil, nil)
 	if err != nil {
 		panic(err)
 	}
 	win.MakeContextCurrent()
-	glfw.SwapInterval(1)
+	// vsync
+	if gio.MainConfig.FramerateLimit == 0 {
+		glfw.SwapInterval(1)
+	} else {
+		glfw.SwapInterval(0)
+	}
 
 	err = gl.Init()
 	if err != nil {
@@ -83,5 +97,9 @@ func main() {
 		} else {
 			fpsCounter++
 		}
+
+		if gio.MainConfig.FramerateLimit > 0 {
+			<-frameTick.C
+		}
 	}
 }
diff --git a/internal/io/config.go b/internal/io/config.go
new file mode 100644
index 0000000..df84c26
--- /dev/null
+++ b/internal/io/config.go
@@ -0,0 +1,20 @@
+package io
+
+import "edgaru089.ml/go/gl01/internal/util"
+
+var (
+	MainConfig struct {
+		WindowWidth, WindowHeight int
+		FramerateLimit            int // 0: vsync, -1: unlimited
+	}
+)
+
+func LoadConfig() (err error) {
+
+	err = util.LoadJSON("main.cfg.json", &MainConfig)
+	if err != nil {
+		return
+	}
+
+	return
+}
diff --git a/internal/util/json.go b/internal/util/json.go
new file mode 100644
index 0000000..bece338
--- /dev/null
+++ b/internal/util/json.go
@@ -0,0 +1,40 @@
+package util
+
+import (
+	"encoding/json"
+	"os"
+)
+
+func LoadJSON(filename string, object interface{}) (err error) {
+
+	file, err := os.Open(filename)
+	if err != nil {
+		return
+	}
+
+	dec := json.NewDecoder(file)
+	err = dec.Decode(object)
+	if err != nil {
+		return
+	}
+
+	file.Close()
+	return
+}
+
+func SaveJSON(filename string, object interface{}) (err error) {
+
+	file, err := os.Create(filename)
+	if err != nil {
+		return
+	}
+
+	enc := json.NewEncoder(file)
+	err = enc.Encode(object)
+	if err != nil {
+		return
+	}
+
+	file.Close()
+	return
+}