In many fields, there is great uncertainty as to whether a new design will actually do what is desired. New designs often have unexpected problems. A prototype is built to test the function of the new design before starting production of a product.

Building the full design is often expensive and can be time-consuming. Sometimes, rather than building the design, figuring out what the problems are, then building another full design, "rapid-prototyping" or "rapid application development" techniques are used for the initial prototypes, which implement part, but not all, of the complete design. This allows manufacturers to rapidly and inexpensively test the parts of the design that are most likely to have problems, solve those problems, and then build the full design.