Whenever I have some free time on my hands, I check StackExchange answers for plagiarism. I am not referring to cross-SE plagiarism, I am looking to check answers posted on SE that have their content plagiarized from other Internet sites.
I initially used to do this the lame way (paste into google, put double quotes, rinse repeat for different sentences). Today I googled "plagiarism checker online" and there's dozens of such software all willing to do this for free! Some do require an account sign-up but that's a non-issue (Guerrilamail ;))
Since I have not used any of those, I am not sure how effective they are. I just ran a check through two of the first hits - SmallSEOTools and QueText. The former wasn't even able to identify the original SE answer from which I copied the text, while the latter correctly did. Grammarly requires a paid plan, however, I am looking for free ones only.
So, I am looking for the most effective free online plagiarism checker, hopefully optimized for StackExchange answers (average length: 1200 characters)
To properly define plagiarism, specifically in the context of StackExchange, it would be when a user posts content - copied from an external resource (different SE answer/off-site resource) - with no attribution (link, textual citation, any sane indication) to the original source whatsoever. For an example, answer A is an example of plagiarism (no visible attribution), while answer B is not (clear attribution).