•In-plane uniaxial anisotropy induced by stress annealing.•Anisotropy probed by broadband ferromagnetic resonance.•Permeability determination from ferromagnetic resonance is non destructive. We report on the broadband characterization of Co74.6Fe2.7Mn2.7Nb4Si2B14 (at%) melt-spun, soft magnetic alloy ribbons after various secondary processing treatments. Ribbons were investigated in the as-cast (melt-spun) condition, after annealing under stress at 50–200 MPa, and after transverse magnetic field (TMF) annealing. The magnetization dynamics of these materials have been studied from 10 to 60 GHz using ferromagnetic resonance (FMR). The in-plane uniaxial anisotropy was determined from the FMR data and permeability extracted for each condition. The permeability determined from broadband FMR was in good agreement with independently determined values using vibrating sample magnetometry and impedance spectrometry of toroidal cores. The effective damping parameter (αeff) of all the samples was close to 0.015 except for the TMF sample, which showed higher damping, possibly due to two magnon scattering.