web performance analysis tool

Yslow is a tool that allows you to analyze the performance of a website and that helps improve the loading time of the page.

YSlow is a tool that measures the “performance” (performance) of websites. Created by Yahoo! Actually, it can also be installed as an extension in the most common browsers, so it is available in Chrome, Safari, Firefox, and others.

In this article we look at it when it was part of the Firefox extension called . However, today the project is available for various browsers and has continued to increase functionality.

The YSlow component allows us to analyze the behavior of the web page we are visiting and offers a multitude of tips aimed at improving download speed. When we install YSlow in Firefox, an icon appears in the lower right corner, which when clicked shows us an analysis of all the external components of the page we are on, along with an efficiency report that covers many more or less interesting aspects. , What:

• Tips to make fewer HTTP connections.
• Add an Expires header
• Gzip components for faster download
• Put the style files in the header
• Put the scripts in the header
• Avoid CSS expressions in the body of the page
• Minimize Javascript script files
• Remove duplicate scripts
• Etc.

All these recommendations, when they must be applied to the site, come with references to the places where they are acting incorrectly and with explanations of what each of the points discussed means.

Apart from the behavior of the page (performance) other reports are offered such as

• Statistics (with the stats button) that offers us a list of the external components of the page and the weight they occupy, if they are cached or not, etc. with a pie chart to see the relative weight of each with respect to the entire page.
• A list of all the external components (with the components button) that informs us of all the external files loaded to view the page, the date they were created, the weight in Kb, the loading time and whether they are compressed.
• A series of reports of interest (in the tools button) in which a verification of the Javascript scripts stands out, with syntax errors, which do not cause bugs in execution time but are badly programmed (this report is offered thanks to , a Javascript checker).
• Comprehensive help on the component (help button)

The YSlow add-on for Firefox is offered by the Yahoo Developer Network and is very useful for developers. We can download it and get more information at:

This project is free software and has its Github page: