ConArg2: A Constraint-based Tool for Abstract Argumentation. ConArg2 is a Constraint-programming tool oriented to the solution of problems related to extension-based semantics in Abstract Argumentation. It exploits Gecode, an efficient C++ toolkit for developing constraint-based systems and applications. The properties required by semantics are encoded into constraints, and arguments are assigned to 1 (i.e.,true ) if belonging to a valid extension for that semantics. Searching for solutions of problems (as enumerating extensions or checking argument-acceptance) takes advantage of well-known techniques as local consistency, different heuristics for trying to assign values to variables, and complete search-tree with branch-and-bound.