MolCa will provide a set of unique online tools for biomolecular computing. The first tool available here is for identifying protein residues associated with a bound ligand. Given a 3D-structure of a protein-ligand complex, it is tricky to identifying all residues surrounding the ligand even with a 3D visualizer. Simply upload your PDB files, MolCa will label those residue in a sequence list and distinguish whether their backbone or side chain atoms are in contact with the ligand. This can be useful for experimental scientists to identify residues for mutagenesis studies.