Recently VPIphotonics developed a new simulation tool, VPItoolkit™ QKD. When used together with VPItransmissionMaker Optical Systems, a simulation environment for classical transmission systems, they represent a powerful R&D environment for the development of QKD systems based on weak-coherent prepare-and-measure protocols, including co-existence scenarios with classical channels. The design environment can serve as a test bed for the development and evaluation of various implementation options of QKD systems and sub-systems, such as pulse shaping, signal recovery and filtering, and others. The toolkit offers capabilities for modeling a wide range of component imperfections by inheriting the versatile numerical approach of VPItransmissionMaker™ Optical Systems (part of VPIphotonics Design Suite™), including thermal noise, ADC quantization noise, RIN, phase noise, dark count rates, afterpulsing, dead time, etc. Also, exploiting the powerful model libraries coming with VPItransmissionMaker™ Optical Systems, the toolkit allows the investigation of various deteriorate effects such as Raman scattering and crosstalk from classical channels in co-existence scenarios. The native sweep and scripting functionality offers a convenient way to optimize simulation parameters such as modulation amplitude, photons per pulse, filter bandwidth, BB84 basis probability, symbol rate, and others. In the webinar we discuss modules for both CV- and DV-QKD including transmitters and receivers, parameter estimation, and secret key rate calculation and show live demos of various application examples.