Speech app design shares many of the characteristics of software design in general, but there are also some aspects unique to voice interfaces—for example, dealing with the issue that speech recognition is always going to be less than 100 percent accurate, and so is less reliable compared with input when using a GUI. Another issue is that, since speech is transient, especially on devices with no visual display, greater demands are put on the user's memory compared with a GUI app.
There are many factors that contribute to the usability of a speech-based app. It is important to perform extensive use case analysis in order to determine the requirements of the system, looking at issues such as whether the app is to replace or complement an existing app; whether speech is appropriate as a medium for input/output; the type of service to be provided by the app; the types of user who will make use of the app; and the general deployment environment for the app.