MolProbity
Structure validation on client-uploaded or PDB ID-specified files, using all-atom contact analysis tools and updated geometrical criteria for phi/psi, sidechain rotamer, and Cbeta deviation
NQ-Flipper
NQ-Flipper recognizes unfavorable rotamers of Asn and Gln residues in protein structures obtained from X-ray crystallography, NMR or modelling studies.
Procheck A program that checks the stereochemical quality of a protein structure
Prosa-web
Quality scores of a protein are displayed in the context of all known protein structures and problematic parts of a structure are
shown and highlighted in a 3D molecule viewer.