Yahoo's YSlow Plug-in Tells You Why Your Site is Slow

Stoyan writes "Steve Souders, performance architect at Yahoo, announced today the public release of YSlow — a Firefox extension that adds a new panel to Firebug and reports page's performance score in addition to other performance-related features. Here is a review plus helpful tips how to make the scoring system match your needs.

Comments

Re:/. gets a D

[JuanCarlosII]

Even better than that, http://developer.yahoo.com/yslow/ gets a D for performance.

Why is this a troll?

[kat_skan]

The Anonymous Coward here is spot on. This thing gives awful, awful advice. Some of these in particular I really hated as a dialup user.

CSS Sprites are the preferred method for reducing the number of image requests. Combine all the images in your page into a single image and use the CSS background-image and background-position properties to display the desired image segment.

This is only a win if your images are tiny. Why are you optimizing for this? Tiny images do not take long to download, even on dialup, because they are tiny. Frankly I would prefer to have all the site's little icons progressively appear as they become available than have to wait while a single image thirty times the size of any one of them loads. Or, perhaps, fails to load, so that I have to download the whole thing again instead of just the parts I have.

Inline images use the data: URL scheme to embed the image data in the actual page. This can increase the size of your HTML document. Combining inline images into your (cached) stylesheets is a way to reduce HTTP requests and avoid increasing the size of your pages.

This is hands down the stupidest idea I have ever heard. Ignoring for the moment that it won't even work for the 70% of your visitors using IE, sending the same image multiple times as base64-encoded text will completely swamp any overhead that would have been introduced by the HTTP headers.

Combined files are a way to reduce the number of HTTP requests by combining all scripts into a single script, and similarly combining all stylesheets into a single stylesheet.

Less egregious than suggesting CSS Sprites, but it still suffers from the same problems. These are not large files, and if they are large files, the headers are not larger.

As described in Tenni Theurer's blog Browser Cache Usage - Exposed!, 40-60% of daily visitors to your site come in with an empty cache. Making your page fast for these first time visitors is key to a better user experience.

What, seriously? Are you really optimizing for your visitors who load one and only one page before their cache is cleared? Even though you "measured... and found the number of page views with a primed cache is 75-85%"?

Add an Expires Header

...

Browsers (and proxies) use a cache to reduce the number and size of HTTP requests, making web pages load faster. A web server uses the Expires header in the HTTP response to tell the client how long a component can be cached. This is a far future Expires header, telling the browser that this response won't be stale until April 15, 2010.

Expires: Thu, 15 Apr 2010 20:00:00 GMT

...

Keep in mind, if you use a far future Expires header you have to change the component's filename whenever the component changes.

And if you ever change something but forget to change the file name, your visitors will have to reload everything on the damn page to get the current version of the one thing you changed. Assuming, of course, they even realize there should be a newer version than the one they're seeing. And assuming that they actually know how to do that.

Put CSS at the Top

While researching performance at Yahoo!, we discovered that moving stylesheets to the document HEAD makes pages load faster. This is because putting stylesheets in the HEAD allows the page to render progressively.

Um. Duh? link elements are not valid in the body. style elements are