Core-shell nanoparticles (NPs) are amongst the most promising candidates in the development of new functional materials. Their fabrication and characterization are challenging, in particular when thin and intact shells are needed. To date no technique has been available that differentiates between intact and broken or cracked shells. Here a method is presented to distinguish and quantify these types of shells in a single cyclic voltammetry experiment by using the different electrochemical reactivities of the core and the shell material. A simple comparison of the charge measured during the stripping of the core material before and after the removal of the shell makes it possible to determine the quality of the shells and to estimate their thickness. As a proof-of-concept two multifunctional examples of core-shell NPs, Fe3O4@Au and Au@SnO2, are used. This general and original method can be applied whenever core and shell materials show different redox properties. Because billions of NPs are probed simultaneously and at a low cost, this method is a convenient new screening tool for the development of new multifunctional core-shell materials and is hence a powerful complementary technique or even an alternative to the state-of-the-art characterization of core-shell NPs by TEM.