The WebSTAR3D web server is a user-friendly online interface for the alignment of RNA 3D structures. The website takes as input two files, each of which can be in either PDB or mmCIF format, containing the desired structures to align, via a PDB code or user upload. In return, the user is presented with a visualization of the aligned structures in Jmol or JSmol, along with the corresponding sequence alignment, and the option to download the nucleotide mapping of the structures and a PDB file containing the aligned, superimposed structures.