Green’s Dictionary of Slang

kidding n.

[kid v. (2)]

the act of teasing, joking; trickery.

[UK]H. Smart Long Odds II 234: ‘Such a shameless bit of ‘kidding’ would have ensured my being hooted off the course at Stockbridge or Croydon’.
[Aus]Duke Tritton’s Letter n.p.: Sometimes I wonder why she married me, and when I ask her, she just smiles and says, ‘It must of been your good looks.’ (Which is kidding as you know I am no oil painting.).
[US]‘O. Henry’ ‘The Fifth Wheel’ in Strictly Business (1915) 67: Just wanted to have some fun kiddin’, I guess.
[US]W.R. Burnett Little Caesar (1932) 28: Can’t you take a little kidding?
[US]J.T. Farrell Gas-House McGinty 50: Never mind incitin’ my clerks to kid with drivers [...] give the calls out and can the kiddin’ business.
[US] Dos Passos USA 6: In the kidding stories of uncles and the lies the kids told at school.
[US]Lait & Mortimer USA Confidential 143: When a national picture magazine publicized the marriage, he couldn’t stand the kidding.
[US]D. Mamet Sexual Perversity in Chicago (1994) 56: All kidding aside ... lookit, I’m a fucking professional, huh?
[US](con. early 1950s) J. Ellroy L.A. Confidential 17: Ed, all kidding aside.

In phrases

kidding on the square (also kidding on the level)

(US) teasing with underlying serious intent.

[US]Van Loan ‘For the Pictures’ in Taking the Count 340: ‘Quit your kidding!’ ‘But I might be kidding on the square.’.
[US](con. 1998–2000) J. Lerner You Got Nothing Coming 394: The threat is only half in jest — what convicts call ‘kidding on the square’.
[US]J. Ridley What Fire Cannot Burn 63: Soledad was kidding on the square. A little jealous, never mind her jokes.