Cosy is an efficient C++ library designed to dynamically break symmetries in SAT problem-solving. It was developed with contributions from the Automata and Applications team and leverages state-of-the-art CDCL SAT solvers by integrating a symmetry controller that complements the CDCL algorithm. Cosy can be seamlessly integrated into most CDCL solvers, enhancing flexibility and performance, particularly for highly symmetrical SAT instances. It is available under the open-source GPL v3 license.