I want to buy a domain, but how can I check if it's been penalized by Google?
 

Algo penalized is the worst cause no way you can recover.

I'm looking for a free online checker if that's the only option.

There is no reliable checker but your first step would be to type site:domain.com and info:domain.com .
If there is no any results while domain is still online then there is a big chance how it's penalized.

Based on my ex and research, some algorithm-penalized sites can be found on Google search, new posts can be indexed in a day, BUT they never rank.

Yes, that is why there is no reliable checker.

Little known site that does it all https://www.spamzilla.io/

it does a complete overview of expired domains but also you can enter your current URL and it will do an overview including any backlinks that are considered spam. I think that's what you may want

Spamzilla is not really something I would use to check a domain like this. It mostly just uses other API's anyway(Majestic, AHREFS, etc). Spamzilla is great for its intended purpose, but this ain't it.

If the site is live, check its Ahrefs + Similarweb and do what Klen suggested. Personally, I wouldn't buy a site that has any age and very little SE traffic (as a % of total). Buy a domain and do it right the first time instead.

if asians had it before you and let it go its crap. ( wayback machine)

What if site: domain populates but info:domain is just other sites?

I think that happens in case of 301 redirects.

Interesting. Thanks Klen

:thumbsup bump for webmaster talk.

I have 2 domains running for more then a month, both in Google search console that says that they are indexed, but when i Google them i don't get any result.

Would it be possible that they don't show the domains because they have "only" and "fans" in the domain name?

The number of DMCA requests can also be an indicator, too many (unresolved) reports will get you a penalty, you can check the number of requests here:

https://transparencyreport.google.co...omains/gfy.com (change the domain in the url)

You can find the reports at the bottom and check whether the pages were removed or not.

Good luck!