Question about EndOfSentence: Found invalid end of sentence "'.".

[dylan-chong]

This tool was created using a thing called 'Hello'.

EndOfSentence: Found invalid end of sentence "'.".

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Are we sure that the above is actually grammatically incorrect? It seems like a perfectly valid sentence to me, and i was not able to find a website that says this is not valid

[edwardwoodward]

It is not grammatically incorrect. It's just a question of style.
In US English, the "correct" style is to place a comma or full stop (period) inside the quotation marks, even if it is not actually part of the quotation. RedPen has adopted this US style. Personally, I think that rule is illogical, and I would recommend ignoring it (but I'm British...)