If you go to the help center, you'll find it written there

don’t ask any questions about [...] [p]roofreading ("are there any mistakes?"), unless the source of concern is clearly specified

but I couldn't find any discussion on meta of the topic. I suspect the above rule was written in the early days of the community and never discussed, so I decided to see what you think:

Q: Are questions of the form "is the above text correct?" on topic or off topic?

P.S. This meta question is relevant, although it covers only one aspect, the spelling