In its crystal structure, the title compound, C(9)H(7)NO(3), forms π-stacked dimers, with a centroid-centroid distance of 3.475 (5) Å between the benzenoid and the 2,4 dicarbonyl oxazine rings. These dimers then form staircase-like linear chains through further π-stacking between the benzenoid rings [centroid-centroid distance of 3.761 (2) Å]. The methyl-H atoms are disordered due to rotation about the C-N bond and were modeled with equal occupancy.