I/I'll tell you what

tell you what

A phrase indicating that the speaker is going to present a suggestion or their opinion on something. I tell you what, this burger might be the best I've ever hard. Tell you what, why don't you go out for a run and I'll watch the kids for a while. I'll tell you what, that was some concert.
See also: tell, what

I/I’ll ˌtell you ˈwhat

,

ˌI know ˈwhat

(spoken) said before making a suggestion: I tell you what — let’s ask Fred to lend us his car.I know what! Why don’t you buy her a CD?
See also: tell, what