How would i check or know if any website gone in penalty after Google update?

Selected answers from the Dumb SEO Questions Facebook & G+ community.

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  A Cirlincione: First, look in webmaster tools for any messages about action by Google. Additionally, download the inbound link list there as well. Review current link profile and see what kind of links you currently have pointing to your site; and to answer the second question, follow the guidelines given by the search giant on how to go about removing spammy links. There is a process and a format to follow. BTW it is long and with no guarantee of success.
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  Reginald Chan: +john matthew Hey mate.
  
  It is hard to know which sites actually get penalty since most of us check on traffic. My traffic dropped pretty bad but picked up again after 7 days. Lucky? Not sure seriously.
  
  Second part is tricky. I usually use tools like ahref or majesticseo and check on the backlinks. Get a list of url pointi g to you and I check one by one.
  
  Alternatively, google will prompt you on webmaster tool on some cases.
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  john matthew: +A Cirlincione ;Hi there, Thanks for reply much appreciated, i agree with you about downloading and deducting the links manual what if i have few time for doing these things did you hear about this software ?http://www.linkdetox.com/benefits/ ?
  
  is anyone in your circle use it, love to hear about the review so that if i can or should try this?
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  john matthew: +Reginald Chan ;yeah i agree Google will send messages in some cases, but if our measurement tool must me exactly the same or at least it should looks the links in same way as Google does? because of  ;few bad or low quality links Google or search engine is considering website back link profile average profile or getting no rankings for the pages which are too relevant and user friendly, those metric did not read by SEO majestic or ahref if so i did not find or use actually both of these web based software!
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  Ranu Jain: Hi John,
  
  Apart from the insights given above, I would like to add my two cents here.
  
  One of the ways to find the penalty is to look for the site rankings and the traffic. If you see any downfall without making any changes on the website then there are chances that your site has been penalized.
  
  To remove the spammy and low quality links, ask site owners to remove your links and if that's not possible, Disavow those links.
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  john matthew: +Ranu Jain ;Thanks Ranu for always natural and easy to do solutions!
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  Ranu Jain: Glad I could help!
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  Guillaume Boucher Bélanger: +john matthew I would not recommend using linkdetox...why? because in the end they probably do the same thing you could easily do on your own.
  
  If you really have 750,000 to get rid of on 5 sites just switch url and it will be cheaper and faster to gain a good ranking this way. But don't take the fall again by subscribing to 750,000 directories.....
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  Jigar Mehta: just setup google webmastertools account and monitoring it and follow their guidelines
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  john matthew: +Guillaume Boucher Bélanger ;hi Guillaume Thanks for reply ! i think you have the experience of using linkdetox.com are you saying i would get directories links automatically when i will run or use the software for deducting bad links and disavow those links? ;
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  john matthew: +Jigar Mehta ;Hi jigar, Thanks for reply  ;but webmaster tools will only give list of links attached to website but does not tell if in what percentage this link affecting or if this link is only bad link for unrelated websites?
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  Guillaume Boucher Bélanger: You should never pay for link removal, because you can do it by yourself easily. That's all :)
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  Guillaume Boucher Bélanger: You can use your webmaster tool to find those links and then look a their credibility. Only thing you have to do is contact the webmaster of thoses pages and ask them for a link removal.