On November 19, 2016 Google has released its Search Quality Rating Guidelines.
On 27 July 2017 Google has released an updated version of its Search Quality Rating Guidelines.
In the past, there has always been a great interest in these guidelines and have been shared among SEO operators as unofficial suggestions and tips.
This time, however, the 160-page PDF was published directly on the Official Google Webmaster Central Blog.
I finded very interesting read this document. We can understand better how Google's "human evaluators" judge our site and so how the search engine wants the content published on the web. It'is a bit like doing a reverse engineering.
While this PDF doesn’t reveals any formulas used for ranking or any secret algorithms, the 160-page document complete with many examples and screenshots. Does offer a endearing view of what the search engine considers as priorities.
Google write "a good search engines give results that are helpful for users in their specific language and localization" so this are their mission. These quidelines can help webmasters and the SEO operators to understand what Google looks for in web pages.
You can download the full version, courtesy of Google, searchqualityevaluatorguidelines.pdf.