From Longman Dictionary of Contemporary EnglishI kid you notI kid you notspokenTRUE used to emphasize that you are telling the truth → kid
Examples from the Corpus
I kid you not• It really was scary - I kid you not.• Of jaundiced varnish, wood-smoke, grease, candle-wax, cigarette smoke and fly-shit. I kid you not.• I manage to earwig a conversation between, and I kid you not, two members of Napalm Death. 