The results screen can be a bit intimidating the first time you see it because there is a lot of information to consume but there are some key pieces of information to look at first.
WebPagetest is a tool that was originally developed by AOL for use internally and was open-sourced in 2008 under a BSD license.
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Web Page Performance Test of Omaha Code.
They are enabled by default on most configurations and are part of the HTTP 1.1 standard but there are times when they will be broken (sometimes unintentionally). Enabling keep-alives is usually just a configuration change on the server and does not require any changes to the page itself and can usually reduce the time to load a page by 40-50%.
Enabling compression for text resources is usually just a server configuration change without requiring any changes to the page itself and can both improve the performance and reduce the costs of serving the content (by reducing the amount of data transmitted).
The image compression check just looks at photo images (JPEG files) and makes sure the quality isn’t set too high. JPEG images can usually be compressed pretty substantially without any noticeable reduction in visual quality.
We use a standard of compressing the images at a quality level of “50” in Photoshop’s “Save for Web” mode but generally you should compress them as much as you can before they start to look bad.
It’s also not uncommon for other data to be included in photos, particularly if they came from a digital camera (information about the camera, lens, location, even thumbnail images) and some of that should be removed from images before being published to a web page (be careful to retain any copyright information).