The 1,2,4-triazine ring of the title compound, C(8)H(13)N(3)O(3), is nearly planar (r.m.s. deviation = 0.019 Å). The imino group is hydrogen-bond donor to the exocyclic O atom at the 5-position of an adjacent mol-ecule, the N-H⋯O hydrogen bond generating a chain parallel to the b axis.