Question: Do you have to say something when you attack the King or the Queen?
Answer:
No, you have no obligation to inform your opponent when you attack the King or the Queen. A player will often say 'check' when attacking the King, but this is a courtesy, not a rule. As for the Queen, there is no convention to say anything : not 'en garde' or 'cherk' or anything else.
A good player will sometimes be annoyed when you say 'check', while a weak player will often be annoyed when you don't say 'check'. Since a beginner may easily overlook that the King is attacked, you can save time saying check, especially when you're not playing with a clock and you don't want to lose time while your opponent considers impossible moves.
One last point : there is no penalty if a player incorrectly claims checkmate. The game continues.
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