There are tools in which you can know many things about a website, its structure, how it is done, what platform, how it is positioned in Google, its ranking, ect.
In Google Chrome I know two excellent extensions, which are:
This is an extension of Google Chrome with which you can know in which platform is made the website and what resources it uses, such as knowing if the website is made in WordPress, Joomla, vBulletin, if it was done in PHP, has Google Analytics, YouTube content, and so on.
With this tool you can know the PageRank of a website without having to consult it on a specific web page, just by entering the website you can realize the PageRank has a website:
In addition this tool has several options in which you can see different things of the site, such as the ranking in Alexa, the Keywords it uses, IP address and much information from a whois and the application also makes a whois to the site a number of links that it has in the search engines, and other important things:
The best Whois service I know so far, very complete, offers you all the information you may need, not like a lot of websites that offer this totally incomplete service:
This is another web with several tools such as being able to ping a website in case you can not access and confirm if it is online, you can make a whois, make a Traceroute to a specific IP, ping, a Port Checker, and other important functions: