How to check UNIQUENESS of Article?

1) For articles the best alternative to copyscape is Plagiarisma or DupliChecker
if it says the content is purely unique and you still aren't impressed you might want to get a readability score done for it. This way you can know whether the text makes sense to most people or not.

2) MS Word is quite possibly the best tool to use what you can do is go to Grammarly and check your content's grammar.

As a general rule your content doesn't have to abide by every single grammatical rule. If it gets the message across and is verified to be unique by reputable tools go with it. As a last resort hire a professional editor to proofread.

Trust me, the only reliable tool to check the quality is: Your eyes.

Having proper articles written is hard to outsource.

Google has implemented things into its algorithm that check the uniqueness of an article far beyond what copyscape checks. Articles that are rewritten from other sources -- making all the same points (but using different wording and swapping synonyms) -- Google can absolutely detect this and devalue links from it. Its the same thing Google uses to detect spun content.

A well written article for SEO arranges facts and makes points in a way that is unique, not found anywhere else on the internet. If someone writes an article from scratch, it's usually good. If your article writers like to rewrite other people's content, have them do a mashup taking 2 or 3 different articles and merging them into one.

Of course -- if the article makes no sense at all, it's fairly worthless other than maybe sticking it on a 2nd tier blog.