What does 'just so you know' mean?

Question

“just so you know” (Urban Dictionary)

What does this mean? And what grammatical role does “so” have?

Answer 1

Just so you know is a pretty ordinary construction, as such things go in English.

Just = "only"
So is the ordinary adverb, employed in the sense "in order that"
*You know" = "you know", "you are aware of"

So:

I provide this information (without being asked) in order that you may be aware of it and thus be spared embarrassment or inadvertent error.

Answer 2

"Just so you know" is nothing more than a snarky, passive aggressive phrase. It means "I don't feel obligated to explain myself to you, but since I want to have the last word and I'm too chicken to tell you to mind your own business, I'm going to explain myself and hope you don't realize that you're being disrespected and patronized. Just so you know." It's the same as saying "Just sayin..."

Answer 3

"Just so you know" is a phrase that is used when giving information you are not obligated to give, or giving information as courtesy.

I deactivated my profile on the dating website, just so you know.

Just so you know, I am not seeing her from the last month.