GTMetrix

GTMetrix is another tool which analyzes your web page. You can use it on the following link:

GTMetrix

Below are some of the reported points by GTMetrix and how you can optimize them.

Specify Image Dimensions

This point can be resolved by enabling the setting Add width/height attributes to images in Nitro > Cache systems > Page cache. Page cache also needs to be enabled.

If you have already enabled the above setting and GTMetrix is still reporting this point, it means that there are hard-coded images in your theme, which cannot be handled by NitroPack. You will recognize these images, if they are not located in /image/cache. Such images need to be manually optimized with an intervention to your OpenCart theme.

Combine images using CSS sprites

This should be optimized with a manual intervention to your theme, since it requires custom CSS code and manually combining images into sprites. This is a point, which cannot be optimized by NitroPack.

Inline small JavaScript

This should be automatically handled by NitroPack, if you have enabled the Improved JavaScript detection. More information can be found in Minification. Make sure to test your website after enabling the experimental features, since they might not be compatible with your theme or installed modules.

Use a Content Delivery Network (CDN)

This should be optimized with a CDN service. NitroPack allows you to sync your server resources with Amazon, Rackspace or a custom CDN via FTP. More information can be found in the CDN section of this documentation.

Use cookie-free domains

To resolve this point, please go to NitroPack > Image Optimization and enable the setting Remove Image Cookies.

Make fewer HTTP requests

This point can be resolved by enabling the NitroPack JavaScript and CSS combination. More information can be found in Minification.

It might not be possible to combine all CSS and JavaScript resources, depending on your theme and installed modules. For example, your website could be loading content from http://www.google-analytics.com or http://fonts.googleapis.com which will not get into the combined files. In such cases in order to optimize this point, you will need to manually remove the code which calls these third-party resources.

You can try to move the JavaScript content to the bottom of the page and enable the defer attribute (more info in Minification). Make sure to test how this works for your website, since it might not be compatible with the hard-coded JavaScript in your theme or modules.

Reduce the number of DOM elements

This point depends mostly on your theme and what modules you have enabled for the front page. NitroPack cannot optimize this point. In order to achieve a higher score, consider reducing the content, which you display to your customers, or switching to a more lightweight theme.