Corpus linguistics and the development of commercial NLP applications are two tightly linked activities. It is hard to conceive fast development of high quality applications without proper tools for inspecting the corpora pertaining the application domain. At the same time, it is hard to conceive reliable corpus analysis tools that do not satisfy the standards of software engineering. In the present paper, we will prove the validity of such a concept by showing how application development at CELI benefited from corpus-oriented tools and how these corpus-oriented tools have been produced as a by-product of the technology developed for real applications.