The FoldX web server is an online tool for evaluating the effect of mutations on protein stability, folding, and dynamics. It calculates the free energy of a macromolecule based on its high-resolution 3D structure, offering functionalities such as stability calculation, proton positioning, water bridge prediction, metal binding site prediction, and complex formation free energy analysis. The server also supports alanine scanning and provides detailed reporting options, including atomic interaction networks, structural and energetic details, and general quality reports. The core functionality is driven by an empirical force field (FOLDEF) that combines various empirical terms to estimate free energy contributions. The server is hosted on a robust infrastructure and can handle multiple protein structures simultaneously. It is accessible via a web interface and offers downloadable executables for local analysis. The FoldX force field is designed for high-throughput structural biocomputing tasks, such as SNP screening and in silico drug lead screening. The article discusses the strengths and limitations of FoldX, emphasizing its accuracy in comparing well-defined structures and its potential for predicting mutational effects.The FoldX web server is an online tool for evaluating the effect of mutations on protein stability, folding, and dynamics. It calculates the free energy of a macromolecule based on its high-resolution 3D structure, offering functionalities such as stability calculation, proton positioning, water bridge prediction, metal binding site prediction, and complex formation free energy analysis. The server also supports alanine scanning and provides detailed reporting options, including atomic interaction networks, structural and energetic details, and general quality reports. The core functionality is driven by an empirical force field (FOLDEF) that combines various empirical terms to estimate free energy contributions. The server is hosted on a robust infrastructure and can handle multiple protein structures simultaneously. It is accessible via a web interface and offers downloadable executables for local analysis. The FoldX force field is designed for high-throughput structural biocomputing tasks, such as SNP screening and in silico drug lead screening. The article discusses the strengths and limitations of FoldX, emphasizing its accuracy in comparing well-defined structures and its potential for predicting mutational effects.