Assuming GRH, we prove an explicit upper bound for the number of zeros of a Dedekind zeta function having imaginary part in [T−a, T+a]. We also prove a bound for the multiplicity of the zeros. Math. Comp. 85(299), 1503–1522 (2016). Electronically published on October 7, 2015. DOI: http://dx.doi.org/10.1090/mcom3031