CPV code 72421000 designates Internet or intranet client application development services in the Common Procurement Vocabulary (CPV 2008), the EU classification used to describe the subject of public contracts.
72421000 is a leaf code — the most specific level of its branch — so it can be used directly as the main CPV code of a contract notice. If it does not quite fit, check the neighbouring codes under 72420000 (Internet development services).