Meta’s Rebalancer is a C++ library for expressing constraints and objectives when assigning objects to resources and finding solutions. It provides a Python interface and Apache 2.0-licensed source. The article highlighted here revisits the official September 21 release; Meta says it uses the tool for about 40 million placement problems daily. The same problem representation can use mixed-integer programming or local search, with large problems mainly relying on the latter. Explorer helps investigate which constraints block assignments. Internal timings reflect particular problem sizes, and local search does not always guarantee a global optimum.