Voltage control and efficient operation remain persistent challenges in modern power systems, particularly due to increasing variation and intermittency among consumers and producers. Despite their central role in supporting voltage stability and efficient power delivery, synchronous generators often have conservative reactive power limits and coarse power loss approximations in optimization tools, hindering optimal system performance. SynGenLib is a Python-based software library that provides detailed steady-state modeling and analysis of synchronous generator and transformer branches to address these limitations, explicitly capturing reactive power capability and power losses. The tool enables accurate evaluation of component selections and optimal operation strategies through detailed simulation and efficiency analysis. SynGenLib employs a single-phase RMS steady-state representation, leveraging Kirchhoff’s voltage and current laws to formulate generator-transformer circuits, solved analytically or via iterative methods as required. Its object-oriented design provides user-friendly data classes for generator and transformer specifications, supporting customizable saturation characteristics. The library calculates reactive power constraints and power losses for the generator stator, rotor, core, friction, and transformer. SynGenLib’s accuracy has been validated against PowerFactory, a commercial software, demonstrating calculation accuracy to the third decimal place and efficient computational performance (∼150 ms for 10,000 power loss points and 100 reactive capability points). SynGenLib was developed as part of the SysOpt research project, which supported industrial case studies in optimal reactive power dispatch and power plant efficiency analysis. It exposes its analytical equations for reactive capability and power loss calculations, enabling seamless integration with other tools and enhancing strategic decision-making for optimal power flow studies, component selection, and plant operations.