The Designer validates a mapplet when you save it. You can also validate a mapplet using the Mapplets > Validate menu command. When you validate a mapplet, the Designer writes all relevant messages about the mapplet in the Output window.
The Designer validates the mapplet pipeline in the same way it validates a mapping. The Designer also performs the following checks specific to mapplets:
The mapplet can contain Input transformations and source definitions with at least one port connected to a transformation in the mapplet.
The mapplet contains at least one Output transformation with at least one port connected to a transformation in the mapplet.