•DSOs need to take care of the increased power electronics-caused harmonic pollution.•A mathematical model for the assessment of radial distribution networks is given.•Pandapower-based open source tool for the (un)balanced harmonic analysis is developed.•The accuracy of the tool is verified against commercial tools on different cases.•The tool is available for running simulations, further verification, and upgrades. With the increasing integration of new technologies, power system operators are facing new operational and planning challenges. Most of these changes are caused by power electronics devices of low carbon (LC) units, resulting in more frequent violations of limits defined in the standards, such as the unwanted occurrence of higher-order harmonics. These aspects indicate that an open source tool, capable of analyzing and estimating future impacts of the above-mentioned phenomena and technologies, would be of great benefit. The paper presents the development of a Phyton-based open source tool as an extension of the existing pandapower library. The upgrade includes the capability of balanced and unbalanced harmonic analysis for LC impact assessment. The technical background and mathematical formulations implemented in the newly developed tool are explained in detail and benchmarked against existing commercial tools showing high accuracy, i.e., the median deviation between the results calculated by the developed and the commercial tool is no larger than 0.21% in the worst-case scenario. In addition to verification, the developed tool is used for the analysis of a real-world network with a high share of LC technologies. The source code of the tool is made available for verification and future updates.