‘Okay.’ can confirm a plan, acknowledge an update or close a conversation. It may also sound distant to a reader who expected enthusiasm. A one-word reply rarely contains enough information to settle every interpretation.
Start with the message it answers. If you wrote ‘The meeting is at eleven,’ an acknowledgment may do the whole job. If you asked ‘How do you feel about the change?’ the same reply leaves a substantive question unanswered. Length matters less than whether the response addresses the purpose.
Next, consider the person’s usual style without treating it as a permanent personality label. Someone who commonly sends brief acknowledgments may be communicating normally. A sudden change can be a reason to check in, but it is still not proof of a particular emotion.
A practical clarification might be: ‘Thanks. Just checking whether eleven works for you, or whether you were only confirming you saw the message.’ That resolves the ambiguity relevant to the plan.
Avoid sending a second paragraph solely to interpret punctuation. Ask for the missing answer when it matters. When the conversation is already complete, let a short reply remain short. Brevity can be sufficient even when it is not expressive.