The paper introduces CASTp, an online tool for locating and measuring pockets and voids on 3D protein structures, with a focus on mapping functionally annotated residues. The updated version of CASTp incorporates functional information from the Protein Data Bank (PDB), Swiss-Prot, and Online Mendelian Inheritance in Man (OMIM). The annotations are mapped to surface pockets, interior voids, and other regions of PDB structures using a semi-global pair-wise sequence alignment method. The study details the methods for mapping annotated residues from Swiss-Prot and OMIM to PDB structures, and highlights the visualization capabilities of the CASTp web server. The results show that the mapping of Swiss-Prot annotations adds significant value to the PDB structures, with a high percentage of annotated residues successfully mapped to functional regions. The improved visualization features, including the JMOL plug-in, enhance user interaction and understanding of protein structures. The availability and accessibility of the CASTp web server and its associated mapping database are also discussed.The paper introduces CASTp, an online tool for locating and measuring pockets and voids on 3D protein structures, with a focus on mapping functionally annotated residues. The updated version of CASTp incorporates functional information from the Protein Data Bank (PDB), Swiss-Prot, and Online Mendelian Inheritance in Man (OMIM). The annotations are mapped to surface pockets, interior voids, and other regions of PDB structures using a semi-global pair-wise sequence alignment method. The study details the methods for mapping annotated residues from Swiss-Prot and OMIM to PDB structures, and highlights the visualization capabilities of the CASTp web server. The results show that the mapping of Swiss-Prot annotations adds significant value to the PDB structures, with a high percentage of annotated residues successfully mapped to functional regions. The improved visualization features, including the JMOL plug-in, enhance user interaction and understanding of protein structures. The availability and accessibility of the CASTp web server and its associated mapping database are also discussed.