Abstract: We define and use a SOS-based framework to specify the transition systems of calculi with name-passing properties. This setting uses proof-theoretic tools to take care of some of the difficulties specific to name-binding and make them easier to handle in proofs. The contribution of this paper is the presentation of a format that ensures that open bisimilarity is a congruence for calculi specified within this framework, extending the well-known tyft/tyxt format to the case of name-binding and name-passing. We apply this result to the -calculus in both its late and early semantics.