One of the most useful applications of gnatcheck is to automate the enforcement of project-specific coding standards, for example in safety-critical systems where particular features must be restricted in order to simplify the certification effort. However, it may sometimes be appropriate to violate a coding standard rule, and in such cases the rationale for the violation should be provided in the source program itself so that the individuals reviewing or maintaining the program can immediately understand the intent.
The gnatcheck tool supports this practice with the notion of a “rule exemption” covering a specific source code section. Normally rule violation messages are issued both on stderr and in a report file. In contrast, exempted violations are not listed on stderr; thus users invoking gnatcheck interactively (e.g. in its GPS interface) do not need to pay attention to known and justified violations. However, exempted violations along with their justification are documented in a special section of the report file that gnatcheck generates.