Eddy current testing (ECT) is a standard technique in industry for the detection of surface breaking flaws in magnetic materials such as steels. In this context, simulation tools can be used to improve the understanding of experimental signals, optimize the design of sensors or evaluate the performance of ECT procedures. CEA-LIST has developed for many years semi-analytical models embedded into the simulation platform CIVA dedicated to nondestructive testing. The developments presented herein address the case of flaws located inside a planar and magnetic medium. Simulation results are obtained through the application of the Volume Integral Method (VIM). When considering the ECT of a single flaw, a system of two differential equations is derived from Maxwell equations. The numerical resolution of the system is carried out using the classical Galerkin variant of the Method of Moments. Finally, the probe response is calculated by application of the Lorentz reciprocity theorem. The theoretical approach will be presented, as well as comparisons between simulation results and measured data obtained from the literature. The second part of the paper shows first results obtained after a GMR-based probe over a magnetic plate. The advantages of this sensor will be discussed and first results presented.