YSlow for Firebug

YSlow is an easy-for-use plugin that allows you to inspect any web page just clicking a button. For me, it is a preliminary step in any web site optimization - an indicator about the site pitfalls.

For example: applying YSlow in the blog page you are reading right now, I got the results presented in the right box (website grades go from 1 to 99 and items values are from A to F). I will not depict every small detail about the java.net blog evaluation, I strongly recommend you to download and use YSlow by yourself before trying to understand that information. I suggest you to apply YSlow against the popular sites like google.com or against your current web project.

For those familiar to sites optimization, I would like to talk about a minor and interesting detail about the expiration header - item #3.

Expires is a Http header that allows you to define when a resource (image, css, ...) will need to be reloaded. It is a String representation of a Date in the format EEE, dd MMM yyyy HH:mm:ss z. There is lots of Java code available on the internet to produce the Expires header, the most part is similar to the following code I used during my experiments:

 	public static void setCacheExpireDate(HttpServletResponse response,
			int seconds) {
		if (response != null) {
			Calendar cal = new GregorianCalendar();
			cal.roll(Calendar.SECOND, seconds);
			response.setHeader("Cache-Control", "PUBLIC, max-age=" + seconds + ", must-revalidate");
			response.setHeader("Expires", htmlExpiresDateFormat().format(cal.getTime()));
		}
	}

        public static DateFormat htmlExpiresDateFormat() {
            DateFormat httpDateFormat = new SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss z", Locale.US);
            httpDateFormat.setTimeZone(TimeZone.getTimeZone("GMT"));
            return httpDateFormat;
        }

With the code, the browser started receiving headers like these:

        Last-Modified:  Sun, 19 Sep 2004 22:06:49 GMT
        Cache-Control:  PUBLIC, max-age=57600, must-revalidate
        Expires:         Thu, 09 Aug 2007 05:22:55 GMT
        Content-Type:   image/gif
        Content-Length: 377
        Date:             Wed, 08 Aug 2007 13:22:55 GMT
        Server:           Apache-Coyote/1.1

It was supposed to be a simple configuration step of my website optimization, but - after trying different values for the headers, including Expires header, Cache-Control and Last-Modified - the YSlow was still saying the Expires header was not present. I got confused and started to navigate on discussions lists and blogs when I finally figured out the problem: YSlow uses the idea of a far future.

A far future Expires header

Well, far future seems to be one of that relatives measures, when for a butterfly it could be 23 hours and for a mountain it could be one million years. So, I suppose the far notion should be pre-defined some way. I didn't find and I confess didn't search too much about the standard values adopted by YSlow, but from my desktop experiences I found it: The YSlow magic number far future is

That's it, everything more than two days seems to be far enough to YSlow - a minor detail in this complex task of websites tunning. And it is not an official information, just an empirical observation. If you need more precise guidance about YSlow, the Chief Performance Yahoo!, Steve Souders, is launching a book entirely dedicated to website optimization - a promising publishing from a company that serves millions of users every day :)

A last and very important advise: don't take decisions based only on YSlow. It is just an indicator, a tool created for Yahoo site optimization that can give you a glimpse about the quality of your web site - a helpful tool that should evolve from now on to become part of the arsenal of tips and tricks for websites tunning.

Comments

• Yes, very nice tool.

  The RFC does not require to send Expires header on 304 responses unless the Expires header value actually changed. YSlow seems to honor that even though there is no Expires header on the 304 response. May be it only considers non 304 responses for the 3rd item.

  Does it honor Cache-Control:max-age alternative to Expires?

  Posted by: ksenji on August 08, 2007 at 07:41 PM

• The subject of a very wonderful and distinct
  I thank you for continuing excellence
  Thank you

  =========================================================================

  ليبيا
  شباب ليبيا
  libya
  منتديات
  منتديات ليبية
  غرائب وحقائق
  أحاديث شريفة
  برامج اسلامية للجوال
  مفاتيح الديجيتل
  الشيرنج
  الرسيفرات
  كتب إسلامية
  خلفيات للموبيل
  الشعر الشعبي
  الصحة والطب
  طب اسنان
  كتب طب اسنان مجانية
  برامج طبية
  تعلم الإنكليزية
  اللغة الفرنسية
  طب الإعشاب
  الخواطرالادبية
  الازياء والمكياج
  تعليم الطبخ
  الاثاث الحديث
  مقاطع كرة قدم
  المصارعه الحرة
  اهداف كوره
  الفوتوشوب
  اروع البرامج
  الدوري الليبي
  خلفيات رياضية
  المصارعة
  كورة عربية
  كرة قدم عالمية
  الدوري الإيطالي
  الدوري الاسباني
  الدوري الإنجليزي
  صور المشاهير
  انواع الحلويات
  افلام كوميدية
  احدث الافلام
  افلام
  التقنية
  تحميل افلام
  برامج
  اخر برامج الجوال
  kaspersky
  أفلام كرتون عربية
  برامج برامج كمبيوتر
  برامج حماية
  برامج اختراق
  برامج صوت
  برامج تحميل برامج احدث البرامج
  محادثة
  خلفيات الطبيعة
  برامج مبايل للتحميل
  اخبار الفن
  احدث الافلام للتحميل
  تحميل افلام رعب
  ترجمةأفلام
  الكامات
  برامج جوال
  برامج محاسبة
  برامج
  kasper
  games
  برامج
  برامج
  انترنت
  برامج صوتية
  شبكات الحاسوب
  خلفيات للويندوز
  تطويرالمواقع
  العاب
  العاب الفيديو
  games
  شفرات
  برامج مسنجر
  خلفيات شاشة
  صور ترحيبيه
  الفوتوشوب
  خلفيات طبيعة
  تطويرالمواقع
  الفوتوشوب
  مقاطع البلوتوت
  مسجات ليبية
  خلفيات
  الفلاش
  التصميم الثلاثي
  برامج الجوال
  العاب الجوال
  فيديو كليب
  مسجات
  ترددات ستالايت
  نغمات
  

  Posted by: libyan on May 30, 2008 at 02:15 PM

This work is licensed under a Creative Commons License.