Modifications of histone tails, including lysine/arginine methylation, provide the basis of a 'chromatin or histone code'. Proteins that con-tain 'reader' domains can bind to these modifications and form specific effector complexes, which ultimately mediate chromatin function. The spindlin1 (SPIN1) protein contains three Tudor methyl-lysine/arginine reader domains and was identified as a putative onco-gene and transcriptional co-activator. Here we report a SPIN1 chemi-cal probe inhibitor with low nanomolar in vitro activity, exquisite selectivity on a panel of methyl reader and writer proteins, and with submicromolar cellular activity. X-ray crystallography showed that this Tudor domain chemical probe simultaneously engages Tudor domains 1 and 2 via a bidentate binding mode. Small molecule inhibition and siRNA knockdown of SPIN1, as well as chemoproteomic studies, iden-tified genes which are transcriptionally regulated by SPIN1 in squa-mous cell carcinoma and suggest that SPIN1 may have a roll in cancer related inflammation and/or cancer metastasis.