Crocodile™ is a security checking tool for router or firewall configurations. The tool supports the security analyst in detecting potential errors in the configuration settings of a router. It also supports serial examination by quickly scanning large numbers of configuration files. Crocodile™ can be easily adapted to individual evaluation criteria, either by specifying evaluation rules in a simple, but powerful rule format or by adding project-specific plug-in modules that dock at the flexible programming interface of Crocodile. Checking reports are generated in hypertext format, which facilitates screening of the checking results and of additional materials, such as suggestions for error elimination or web links to relevant pages of the router manual.