Skin permeability of chemicals, usually reflected using the logarithm form of skin permeation rate, log Kp, is a critical parameter used by medicinal chemists, formulators and toxicologists. Medicinal chemists consider skin permeability of dermal active pharmaceutical ingredients in an effort to deliver the desired dose; formulators need to understand the skin permeation rate in order to create an effective and safe cosmetic product, while toxicologists care for minimizing skin permeation rates in order to prevent potentially hazardous effects of commercial chemicals. Toxicologists also have to take skin permeability rate into account when carrying out chemical risk assessments or alternatives assessments. Experimental methods for testing skin permeability are cost-prohibitive and as a result fast and accurate predictive methods are highly desirable. Most incumbent tools for log Kp prediction rely on physicochemical and structural descriptors. However, these models are often limited to structurally similar chemical analogs(1) and some have low accuracy of prediction in external validation(2). The ToxSpec module for prediction of log Kp relies on simulations of biochemical interactions of chemicals with the epidermis. It takes into account ionization, which strongly influences the permeation rate. The model is extensively validated and widely applicable to industrial and pharmaceutical chemicals.