Hydroxybenzotriazole (abbreviated HOBt) is an organic compound that is a derivative of benzotriazole.  It is a white crystalline powder, which as a commercial product contains some water (~11.7% wt as the HOBt monohydrate crystal). Anhydrous HOBt is explosive.
It is mainly used to suppress the racemization of single-enantiomer chiral molecules and to improve the efficiency of peptide synthesis.