PageSpeed Insights

Frequently Asked Questions

  1. How is PageSpeed Insights different from the PageSpeed browser extensions? Which should I use?
  2. How does PageSpeed Mobile analysis work? Does it use a real mobile device?
  3. How does PageSpeed Mobile analysis differ from regular PageSpeed analysis?
  4. Some of the suggestions differ from the PageSpeed browser extensions. Why?
  5. I changed my site! Why doesn't PageSpeed Insights see the new version?
  6. How much does someone need to know about web development before he/she can use PageSpeed Insights?
  7. Why is PageSpeed Insights open source?
  8. What rules is PageSpeed Insights based on? Who created them? Why should someone trust them?
  9. You spot a lot of errors in my page but they conflict with the guidance I am getting from other site speed optimization tools. Why should I trust PageSpeed Insights more?
  10. Some of PageSpeed Insights' recommendations seem to go against certain design and development practices. Does Google think that only speed is important?
  11. Are PageSpeed Insights' recommendations more applicable to Google's applications than to the average website?
  12. Are there any restrictions in using PageSpeed technology?
  13. Why can't I find the PageSpeed Critical Path Explorer anymore?
How is PageSpeed Insights different from the PageSpeed browser extensions? Which should I use?
PageSpeed Insights provides similar analysis online, and as browser extensions for Chrome and Firefox. The PageSpeed browser extensions can be used to analyze web pages not accessible from the public Internet, such as those in a corporate environment. The PageSpeed browser extensions can also be used to analyze pages that require you to log in or interact with the page.
Does PageSpeed Insights use a real device?
PageSpeed Insights' analysis does not use real devices. PageSpeed Insights fetches a site with a webkit renderer (the same rendering engine that powers Chrome and Safari) that emulates both mobile device and desktop devices.
How does PageSpeed Mobile analysis differ from regular PageSpeed analysis?
PageSpeed Mobile analyzes the mobile version of a page and tailors suggestions based on the characteristics of mobile networks and mobile devices. For instance, since mobile device CPUs are less powerful than desktop CPUs, suggestions that reduce CPU consumption (for instance JavaScript Parse time) are featured more prominently in the PageSpeed Mobile results.
Some of the suggestions differ from the PageSpeed browser extensions. Why?
PageSpeed Insights uses a different rendering engine and user agent, which may impact the content being fetched for a site.
I changed my site! Why doesn't PageSpeed Insights see the new version?
PageSpeed Insights caches results for a short period of time. PageSpeed Insights should see any changes you've made within a few minutes. If you want instant analysis, please use the PageSpeed browser extensions.
How much does someone need to know about web development before he/she can use PageSpeed Insights?
We assume that webmasters who are interested in improving their site's performance will probably have fairly advanced knowledge of web development techniques. Some PageSpeed Insights rules are based on basic principles of web development; others are based on more advanced features. It is helpful to have some knowledge of web hosting technologies, HTTP, JavaScript and CSS. However, extensive documentation is also provided, so anyone can follow PageSpeed's recommendations.
Why is PageSpeed Insights SDK open source?
We deeply believe in the importance of the open-source model. By making PageSpeed open source, we allow anyone to see what PageSpeed's performance rules check for, and to suggest improvements. By encouraging feedback and patches, we believe that PageSpeed will become more useful and accurate over time.
What rules is PageSpeed Insights based on? Who created them? Why should someone trust them?
Many of the rules used by PageSpeed Insights came out of recommendations of blog posts and articles published by developers in the web community. Other rules were added by developers at Google based on research and internal use by Google applications.
You spot a lot of errors in my page but they conflict with the guidance I am getting from other site speed optimization tools. Why should I trust PageSpeed Insights more?
We would like to learn more on where you saw a discrepancy between the tools. Send a message to our discussion group.
Some of PageSpeed Insights' recommendations seem to go against certain design and development practices. Does Google think that only speed is important?
Since PageSpeed is a performance optimization tool, its recommendations are biased in favor of speed. However, we recognize that web development is complex, and our suggestions might be restrictive for an individual web site. You have to consider the tradeoffs for your own application: some of PageSpeed's recommendations take substantial effort to implement, so you need to evaluate the cost of making changes vs. the benefit the rule would have on your page. Our goal is simply to point out the issues that you should consider fixing.
Are PageSpeed Insights' recommendations more applicable to Google's applications than to the average website?
No. The advice given by PageSpeed is not specific to Google; it should improve the performance of any web page. Of course, pages that are slower have more to gain from PageSpeed's recommendations.
Are there any restrictions in using PageSpeed Insights technology?
The PageSpeed Insights code base is governed by the Apache 2.0 Open Source License. You can use PageSpeed Insights as determined and allowed by the license.
Why can't I find the PageSpeed Critical Path Explorer anymore?
The critical path explorer tool is no longer available as part of PageSpeed Insights. Although the critical path is important for understanding web performance, we have decided to re-think the feature in PageSpeed Insights. In the meantime, we suggest following the recommendations under the new Eliminate external render-blocking Javascript and CSS in above-the-fold content rule in PageSpeed Insights which lists the critical path resources for the page.

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