How to know that google has penalized any particular site. Is there any free online tool available? Thank you in advance for reply.
Suddenly lost positions/disappears in SERPs is one thing to be aware of. I don´t know any kind of tools for that, but i will search my sites daily and see how my sites are doing. And if there is something wrong I will take immediate actions to solve what´s going on..
Sometimes Google's Webmaster tools will give you some idea. However mostly it comes as a massive site wide slap down on your rankings.
Yes, the best way is check your SERP, if its dropped suddenly then it means your website is penalized or affected by Google.
If your website doesn't have any adsense anymore. or if not, google will have an email about the violations. like me, google emailed me about the keyword stuffing.
type into google info:domain if nothing comes up your site has been banished, also if teh pr of teh site is n/a grey bar then likely it has been punished unless it is a new site
Please look into the following points - 1. Sudden Google referral traffic drop 2. Huge differences in rankings if you query general search and a single database. 3 Your domain is not #1 for [yourdomain.com] search. 4. [site:yourdomain.com] returns 0 results
You may be interested in this article which gives an opinion of why they aren't much good to you http://www.seozen.com/penalty-checker-tools/