I will discuss recent progress in computing one-loop partition functions of strings in type II backgrounds with RR flux. The backgrounds we focus on are relevant for holographic setups with well-understood gauge theory duals. The computation of certain observables in the QFT duals can be done using supersymmetric localization to a matrix model. Using string theory, we will compute the expectation value of BPS Wilson loop operators in gauge theories and determine non-perturbative corrections to sphere partition functions and compare with QFT predictions when available.