It's probably a question of personality, custom and habit, but I tend to write like I speak (some would say "no, you speak like you write" :-) in any forum, including Slack, sometimes in defiance of the cultural norms of the audience.

It leads to something of a reputation for verbosity, but never the accusation of ambiguity or excessive terseness. I don't think anyone's ever said to me, "What did you mean by that two-word reply?"