Vulnerability functions describe the expected loss for a given ground shaking intensity level and are an essential component in probabilistic seismic risk assessment. This manuscript presents a novel open-source platform for the derivation of analytical fragility and vulnerability models, covering state-of-the-art methodologies, and addressing critical issues in vulnerability modelling such as uncertainty propagation, validation/verification of results and sufficiency/efficiency of intensity measure types. This framework is divided into six modules designed to guide users through the different stages of analytical vulnerability modelling from the selection of ground motion records to the validation and verification of the models. The platform was implemented in the Python programming language and it is freely accessible through a public GitHub repository. A graphical user interface is included with the toolkit and is intended to be a general-purpose method for modellers to interact with the VMTK. Experienced users are encouraged to use Python’s scripting capabilities to explore all the features of the VMTK source code and to contribute to future releases of the toolkit.