We describe a toolkit to support the use of predicate diagrams, a representation of predicate abstractions that includes annotations for proving liveness properties. Centered around a graphical editor for drawing predicate diagrams, proof obligations for proving correctness of the abstraction w.r.t. TLA+ system specifications can be generated, correctness properties expressed in temporal logic can be verified by model checking, and counterexamples can be visualized. The toolkit also supports stepwise development of systems, based on a notion of refinement of predicate diagrams.