*MolProbity* is a web-based structure validation service designed to evaluate the quality of protein and nucleic acid models at both global and local levels. It relies on optimized hydrogen placement and all-atom contact analysis, complemented by updated covalent-geometry and torsion-angle criteria. The service provides a user-friendly interface for uploading coordinate files, adding and optimizing hydrogen atoms, and selecting validation analyses. Results are presented in charts and graphical forms, aiding manual rebuilding. Key features include all-atom contact analysis, torsion-angle combinations, covalent-geometry analyses, and nucleic acid-specific analyses. *MolProbity* also offers standalone software for correcting identified errors and tools for interface analysis, protein loop fitting, and file conversion. Since its introduction in 2002, *MolProbity* has significantly improved the quality of crystallographic models, as evidenced by the decreasing median clashscore and percentage of incorrect Asn/Gln/His flips over time. The service is freely available for download and can be run as a local server, providing access to command-line tools and scripts for batch processing.*MolProbity* is a web-based structure validation service designed to evaluate the quality of protein and nucleic acid models at both global and local levels. It relies on optimized hydrogen placement and all-atom contact analysis, complemented by updated covalent-geometry and torsion-angle criteria. The service provides a user-friendly interface for uploading coordinate files, adding and optimizing hydrogen atoms, and selecting validation analyses. Results are presented in charts and graphical forms, aiding manual rebuilding. Key features include all-atom contact analysis, torsion-angle combinations, covalent-geometry analyses, and nucleic acid-specific analyses. *MolProbity* also offers standalone software for correcting identified errors and tools for interface analysis, protein loop fitting, and file conversion. Since its introduction in 2002, *MolProbity* has significantly improved the quality of crystallographic models, as evidenced by the decreasing median clashscore and percentage of incorrect Asn/Gln/His flips over time. The service is freely available for download and can be run as a local server, providing access to command-line tools and scripts for batch processing.