FAQs: Performance Suggestions

Visual SEO Studio "Performance suggestions" are mostly built upon Steve Souders' research on web performance ("High performance websites" and "Even faster websites"); the threshold used are based on publicly available statistics on page size, number of DOM elements, etc...

The single tab sheets report mercilessly pages based on a binary decision, whether they exceed or not the given threshold (thresholds can be customized from Preferences... menu option), so a better way to assess the overall impact of each single issue is looking the each dedicated histogram.

Each single measure has also to be taken with a grain of salt, because there are optimization techniques that may worsen a single measurement, for the sake of better performances.
For example:

• inlining CSS critical path increases the HTML page size, but makes the page render faster (or at least makes them be perceived loading faster)
• HTTP/2 might increase TTFB (Time to First Byte) because it packs more responses together, but afterward the browser will find its cache pre-populated
• etc..

Note: the Images inspector tool also gives valuable information about image sizes.

Performance Suggestions is not meant to substitute tools like WebPageTest, but rather to complement them.
The differences are several:

• Visual SEO Studio does a great job on assessing the whole site overall performance, inspecting all site pages.
  Tools like WebPageTest are great to inspect a single page in greater detail.
• WebPageTest, GTMetrix (and PageSpeed insight, online version) work from a remote IP (WebPageTest permits to partially customize the location from where the test is run).
  Visual SEO Studio runs from the local machine.
• WebPageTest works inspecting the browser events (first rendering, dom completion, complete load time....) and is probably the best tool to understand performance issues for a single page.
  Visual SEO Studio concentrates on Saunders' general best practices and single measures over the whole site.
• Most of the tools mentioned, along with the Network dev tool that comes with modern browsers, can analyze the single page entire "waterfall" of a page HTTP requests.
  Visual SEO Studio cannot do it as today it downloads only a subset of page resources.

Overall Visual SEO Studio does a great job inspecting single measures, like no other tool does (e.g. number of DOM elements, DOM depth, ...) and some of them are really helpful, but again, its best value is it's ability to inspect them over the entire site.

It really depends on each specific case. As a general rule of thumbs, experience taught us that if they are reported as issues, the first things to look at are duplicate script tags.
The reasons are:

• Even if thanks to browser caching a duplicate script is downloaded only once, each script is executed each time it is encountered.
• When the browser downloads or executes a script, it completely blocks page rendering and often parallel download of other resources (using attributes defer or async can postpone script execution).

So probably the most valuable reports in Performance Suggestions are the ones dedicated to the scripts - blocking scripts in particular - and CSS blocks, but each site has different priorities.
For example if a site main issue is having huge page size (rarely the most urgent issue) due to a very bad template, that should be fixed first.
Always check how widespread is each issue using both the percentage reported over the whole pages, and even more important how each measure is distributed in the related histogram graph.

There is a significant difference between those tools and Visual SEO Studio's "Performance suggestion": while those ones do inspect a single page (more often than not the Home Page), Visual SEO Studio inspects the whole site pages.

For example here is a real-world case: the download time for the home page is 278 ms, but the mean time is around 1500 ms.

Histogram: Download Time

The performances of a single page are not a good indicator in case of sites with thousands of pages or more. Visual SEO Studio enables you to better understand the overall website performances and locate the pages that need your attentions the most.

The quickest way is:

• Select the "Duplicate script URLs" tab;
• Select the "Page CSS/JS files" bottom pane tab;
• Sort by Absolute URL

Now duplicate URLs are much easier to spot.