To evaluate a software specification for its performance potential, it is necessary to supply additional information, not required for functional specification. Examples range from the execution cost of operations and details of deployment, up to missing subsystems and layers. The term "completions" is used here to include all such additions, including annotations, component insertions, environment infrastructure, deployment, communication patterns, design refinements and scenario or design transformations which correspond to a given deployment style. Completions are related to the purpose of evaluation, so they are tailored to describing the performance at a suitable level of detail. Completions for evaluating other attributes such as reliability or security are also possible. The paper describes how completions are added to a specification regardless of the language used (provided that it describes the system behaviour as well as its structure), and experience with completions in Use Case Maps.