LassoProt collects information about proteins and other (bio)polymers with lassos. LassoProt detects loops (closed by cysteine, as well as amide, ester, thioester and other bridges) in a given (bio)polymer, determines surfaces of minimal area spanned on such loops, and analyzes if and how termini of the polymer intersect these minimal surfaces. The server enables users to analyze new structures and includes a database, which presents extensive information about previously analyzed proteins with lassos.