Naphthyridine-based inhibitors were synthesized to yield a potent and cell-active inhibitor of casein kinase 2 (CK2). Compound 2 selectively inhibits CK2⍺ and CK2⍺’ when profiled broadly, making it an exquisitely selective chemical probe for CK2. A negative control that is structurally related but lacks a key hinge-binding nitrogen (7) was designed based on structural studies. Compound 7 does not bind CK2⍺ or CK2⍺’ in cells and demonstrates excellent kinome-wide selectivity. Differential anti-cancer activity was observed when compound 2 was profiled alongside a structurally distinct CK2 chemical probe: SGC-CK2-1. This naphthyridine-based chemical probe (2) represents one of the best available small molecule tools to interrogate biology mediated by CK2.