A library management system may compare contracts between programming libraries to identify unions, intersections, and differences between libraries. The management system may have a contract analyzer that may remove the contract definition from an existing library to form a library contract. The library contract may be managed as a first class item within a programming environment, and may be used as a reference for comparing existing and new versions of the library. The library management system may create reference libraries for programmers to write applications using two or more intersecting libraries, among other uses.