WC3 standards is the standards for the html code on the sites. When we make our site there can be many code errors which don’t meddle the function of the site but they are extra so it is good for you that you must know such code errors and remove them so that your side function well in the search engine. Go to validator.w3.org and put the url of the pages of your site and it shall scan the pages for such errors and remove them.
This is very useful site. You must know the cost per click of ads. This shall tell you the CPC (cost per click) of the keywords of any site. You can check 5 keywords or sites per day and if you are premium member (paid member) then you can check as much as you can with some additional useful information. To avoid maximum clicks you better put a shortcut url right at the beginning like www.semrush.com/info/www.site.com
• Seo Quake
This is the plugin that can be used with chrome and firefoxbrowsers. That shall show the different necessary details on the tool bar of every site you open. It shall show you the number of indexed pages (pages that are indexed by google means that google know about), Page Rank, whois information of the site (data about site’s owner and when the domain is bought and when it is going to expire etc), alexa ranking (alexa is the site that ranks that site among all sites on internet), semrush ranking, complete diagnosis is the site andkeyword density (percentage the keywords are used in text, if this percentage is more than 5% it may be called keyword spamming or keyword stuffing and will lead to the disabling of your account) etc.