Beside the native-code compilation, GNU Prolog offers a classical interactive interpreter (top-level) with a debugger.

The Prolog part conforms to the ISO standard for Prolog with many extensions very useful in practice (global variables, OS interface, sockets,...).

GNU Prolog also includes an efficient constraint solver over Finite Domains (FD). This opens contraint logic programming to the user combining the power of constraint programming to the declarativity of logic programming.