What Is Yslow And How Do You Interpret Your Yslow Result And Strategies To Improve It?

When it comes to the website’s performance, there are many analyzing tools available. Yslow is one of the trusted online analyzing tools that provide suggestions to improve its performance.

Here, we will cover every detail you need to know about Yslow, including what Yslow is, how it grades a website, and how to run a test on Yslow. 

Yslow banner

We will also find out how you can improve your website’s performance with RabbitLoader. 

Note: This service is no longer active and the browser extensions for Yslow have been depreciated. 

What Is (was) Yslow? 

Yslow is an open-source website performance analyzing tool, available as  browser extensions for all major browsers, it’s developed by Yahoo to help website owners or developers determine a website’s performance. 

Yslow provides grades for websites based on 23 criteria which is then converted into the overall grade for the website.  

Let’s See the list of 23 criteria for Yslow:

  1. Use a CDN
  2. Minimize HTTP requests
  3. GZIP components
  4. Add expires headers
  5. Reduce DNS lookups
  6. Avoid empty src or href
  7. Make fewer HTTP requests
  8. Minify JavaScript and CSS
  9. Avoid URL redirects
  10. Put CSS at the top
  11. Make AJAX cacheable
  12. Remove duplicate JavaScript and CSS
  13. Put JavaScript at the bottom
  14. Avoid alphalmageLoader filter
  15. Don’t scale the image in HTML
  16. Use cookies-free domain
  17. Reduce cookie size
  18. Make JavaScript and CSS external
  19.  Make favicon small and cacheable
  20. Configure entity tags
  21. Use GET for AJAX requests
  22. Avoid CSS expressions
  23. Reduce the number of DOM elements 

How does Yslow grade a website?

In Yslow, you can see a grade for each rule ranging from A to F. An A grade is considered the best performance and equivalent to 90-100, while an F grade is considered a failure. Let’s see how Yslow grades the rules.

Grade Corresponding Score 
AMore than 90
FLess than 50

How To Run A Yslow Test?

In order to analyze the PageSpeed performance of a website in Yslow, first you need to download the Yslow browser extension for your browser. Once the download is completed, you need to follow the below steps to run a PageSpeed performance test in Yslow. 

yslow performance test
  • Put the website’s URL in the browser for checking the speed performance.
  • Click on the “Run Test” button and wait for some time.
  • Once Yslow analyzes the PageSpeed performance of the given website, you can see a report card. 

Improve Website’s Performance With RabbitLoader

A fast-loading website is an essential factor in terms of user experience and SEO rankings. However, speed optimization can be stressful for a webmaster without a development team.

To avoid the technical aspect many webmasters use different plugins for each aspect of the website optimization, which end up harming the website’s performance as these plugin conflict with one another. 


Get The Best PageSpeed Score

For Your WordPress Website

All in One Optimization Plugin
No Coding Knowledge Required

Using RabbitLoader can help you boost your Yslow score as well as your Google PageSpeed score and GTmetrics score by improving your website’s speed performance & visual stability. 

Let’s explore the top optimization techniques required for a lightning fast website and how RabbitLoader can implement these to enhance your website’s PageSpeed performance. 

  • Implement Caching Mechanism

  • Minifying The Resource Files

  • Html, CSS, And JavaScript Compression 

  • CSS Optimization

  • Javascript Optimization

  • Image Optimization

Use Caching Mechanism

The most traditional web optimization technique is using an efficient caching mechanism. Several caching mechanisms are available, but browser caching and CDN caching are the most effective techniques for improving a website’s speed performance.

Both browser caching and CDN caching are used to minimize the HTTP request to the origin server. In the browser caching mechanism, the website’s static contents are stored in the browser cache, whereas in CDN caching, these static contents are distributed among the proxy/ edge server to reduce network latency.

caching mecanishm

RabbitLoader implements both, a browser caching mechanism with an efficient caching policy to enhance your website’s performance and boost the PageSpeed score.

RabbitLoader has a premium Content Delivery Network (CDN) which has 300+ edge servers. So, by distributing the static content among 300+ edge servers, it can significantly reduce the network latency, resulting in an improvement in website’s loading speed. 

Minifying The Resource Files

Minifying resource files such as HTML, CSS, and JavaScript can significantly improve page load time by reducing the total page file size. Minification involves removing unnecessary characters from the coding file without changing the functionality.

minify resources

Manually minifying these resource files can be daunting if your website is large. However, when you use RabbitLoader, you don’t need to minify the resource files one by one. RabbitLoader will remove all unnecessary characters from your coding files and reduce the page size, improving the core web vitals performance especially the loading speed.

HTML, CSS, And JavaScript Compression 

HTML, CSS, and JavaScript compression is another web optimization strategy for reducing your website’s page file size. It minimizes code redundancy by replacing the repeated string variable with a single pointer.   

Html css js compression

There are two ways you compress your resources file: GZIP compression (traditional method) or Brotli compression(modern method). RabbirLoader uses the modern Brotli algorithm and compresses your resource file, reducing your page size and improving the loading time of your website. 

CSS Optimization

If you want to achieve a desirable PageSpeed score, you can’t avoid CSS optimization. There are three ways to optimize your CSS file: reducing unused CSS, minifying CSS files, and generating critical CSS.

CSS optimization requires expertise in HTML and CSS. However, when you are using RabbitLoader, it can optimize your CSS file within a few clicks and help you achieve a good PageSpeed score or grade.    

JavaScript Optimization

JavaScript optimization is an effective strategy for improving a website’s PageSpeed performance. You can optimize the JavaScript files by deferring the non-critical JavaScript function after splitting the JavaScript code along with the JavaScript minification.  

Image Optimization 

Being an asset of your website, sometimes, an unoptimized image can negatively impact the website’s PageSpeed performance by increasing total blocking time. The best way to optimize the image is to convert them into a next-gen format: WebP and AVIF format.

next gen formats

Several tools are available online to convert JPEG and PNG images into the next-gen format. But converting these images one by one can be daunting, especially when you have tens of thousands of images.  

The best practice is to use RabbitLoader to save time. RabbitLoader optimizes your high-resolution PNG and JPEG images without harming their original quality by converting them into modern web formats. 


Manually optimizing a website is a delicate process that requires extensive coding knowledge. However, RabbitLoader makes this process the easiest one by its all-in-one optimization techniques. 

Thus, if you want to boost your website performance grade in Yslow, Google PageSpeed Insights, and GTmetrix, RabbitLoader is the best option for you. Instead of investing your time in ten different plugins, try RabbitLoader’s free version today! 


Get The Best PageSpeed Score

For Your WordPress Website

All in One Optimization Plugin
No Coding Knowledge Required