  Bad requirements quality can cause expensive consequences during the software
development lifecycle, especially if iterations are long and feedback comes
late. %-- the faster a problem is found, the cheaper it is to fix. This makes
explicit the need of a lightweight detection mechanism of requirements quality
violations. We aim at a light-weight static requirements analysis approach that
allows for rapid checks immediately when requirements are written down. We
transfer the concept of code smells to Requirements Engineering as Requirements
Smells. To evaluate the benefits and limitations, we define Requirements
Smells, realize our concepts for a smell detection in a prototype called Smella
and apply Smella in a series of cases provided by three industrial and a
university context. The automatic detection yields an average precision of 59%
at an average recall of 82% with high variation. The evaluation in practical
environments indicates benefits such as an increase of the awareness of quality
defects. Yet, some smells were not clearly distinguishable. Lightweight smell
detection can uncover many practically relevant requirements defects in a
reasonably precise way. Although some smells need to be defined more clearly,
smell detection provides a helpful means to support quality assurance in
Requirements Engineering, for instance, as a supplement to reviews.
