The most widely studied language for expressing statements in the context of Zero-Knowledge (ZK) proofs is arithmetic circuit satisfiability. In this talk we present circom, a programming language and a compiler that allows the programmer to provide a low-level description of the arithmetic circuit together with an effective way to execute it. Challenging constraint manipulation and analysis problems will be introduced as well as some safety properties of circom programs that need to be checked. New language features focused on enhancing security will be discussed.