Development of a preliminary version of a software system in order to allow certain aspects of that system to be investigated. Often the primary purpose of a prototype is to obtain feedback from the intended users; the requirements specification for the system can then be updated to reflect this feedback, and so increase confidence in the final system. Additionally (or alternatively) a prototype can be used to investigate particular problem areas, or certain implications of alternative design or implementation decisions.

The intention with a prototype is normally to obtain the required information as rapidly as possible and with the minimum investment of resources, and it is therefore common to concentrate on certain aspects of the intended system and completely ignore others. A prototype may for example be developed with no concern for its efficiency or performance, and certain functions of the final system may be entirely omitted. It must however be realistic in those aspects specifically under investigation.